changed river roughening
This commit is contained in:
Grimsace
@@ -0,0 +1,609 @@
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package main
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import (
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"image"
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"image/color"
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"math"
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"math/rand"
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"runtime"
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"sync"
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"github.com/ojrac/opensimplex-go"
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)
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// rivers.go
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//
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// New river roughening implementation that uses the heightmap to clip river edges,
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// occasionally creates islands, and is designed to be efficient and multithreadable.
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//
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// This file exposes one main function intended to be called from the river generation
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// pipeline in place of per-pixel painting: `RasterizeAndRoughenRiver`. It:
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// - rasterizes the river centerline into a local mask (bounding box)
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// - computes a fast distance field (chamfer approximation) from the centerline
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// - evaluates a heightmap-aware stochastic rule to remove/add edge pixels to roughen
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// - occasionally grows islands inside the river
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// - writes final water pixels back to the provided canvas and updates the provided isWater map
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//
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// Usage (conceptual):
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// addedPixels := RasterizeAndRoughenRiver(canvas, path, riverWidthPx, heightmap, isWater, seed)
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//
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// NOTE: Because the project already contained a `drawCircle` helper, this new pipeline
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// is implemented as standalone routines in this file. To use it, replace the existing
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// per-circle painting logic in `GenerateRivers` with a call to `RasterizeAndRoughenRiver`.
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//
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// The parameters below were chosen conservatively; tweak them to taste.
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type riverParams struct {
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EdgeBandRatio float64 // fraction of river radius used for roughening band (e.g. 0.6)
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RoughnessStrength float64 // 0..1 how aggressive clipping is at the edge
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IslandAttemptProb float64 // chance per-river to attempt islands
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IslandSeedChance float64 // chance per-water-pixel to become an island seed candidate
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MinIslandSize int // minimum island pixel count
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MaxIslandSize int // maximum island pixel count
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WaterLevelBias float64 // baseline water level in normalized height units [0..1]; small bias subtracted to favor water
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NoiseFrequency float64 // frequency for simplex noise
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KeepInnerFraction float64 // fraction of inner radius always kept as channel (0..1)
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MaxWorkers int // concurrency limit (0 means runtime.NumCPU())
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MinWidthPx float64 // minimum river width in pixels (for sin wave amplitude calculation)
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MaxWidthPx float64 // maximum river width in pixels (for sin wave amplitude calculation)
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}
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// computeSinWaveEdgeOffset computes the radial offset for river edge roughening
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// using dual sine waves. The larger wave has amplitude based on the difference
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// between max and min river widths, and the smaller wave is a quarter of that amplitude.
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// This creates realistic undulating river banks with both large and small-scale variations.
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func computeSinWaveEdgeOffset(absX, absY int, largeAmplitude, smallAmplitude float64) float64 {
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// Use position to create phase for the sine waves
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// Position phase creates variation as we move through the image
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positionPhase := float64(absX)*0.008 + float64(absY)*0.012
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// Large wave: slower frequency for major width variations along the bank
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largeWave := math.Sin(positionPhase) * largeAmplitude
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// Small wave: faster frequency for subtle and natural bank details
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smallWave := math.Sin(positionPhase*3.5) * smallAmplitude
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// Return combined offset
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return largeWave + smallWave
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}
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// RasterizeAndRoughenRiver rasterizes a river path, roughens edges using the heightmap and dual sin waves,
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// optionally creates islands, paints the final water into `canvas`, and marks pixels in `isWater`.
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// It returns a slice of image.Point containing all newly added water pixels for this river.
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//
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// Parameters:
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// - canvas: destination image (will be modified)
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// - path: ordered centerline points for the river
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// - riverWidthPx: nominal width in pixels
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// - heightmap: heightmap image used to guide roughening (expects 0..1 grayscale via RGBA() conversion)
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// - isWater: map used to record already-water pixels (prevents painting over lakes/rivers). This map will be updated.
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// - seed: random seed to make generation deterministic
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// - minWidthPx: minimum river width in pixels (used for sin wave amplitude calculation)
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// - maxWidthPx: maximum river width in pixels (used for sin wave amplitude calculation)
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func RasterizeAndRoughenRiver(canvas *image.RGBA, path []image.Point, riverWidthPx float64, heightmap image.Image, isWater map[image.Point]bool, seed int64, minWidthPx, maxWidthPx float64) []image.Point {
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if canvas == nil || len(path) == 0 || riverWidthPx <= 0 {
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return nil
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}
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// Default parameters - tweak as needed
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params := riverParams{
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EdgeBandRatio: 0.6,
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RoughnessStrength: 0.65,
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IslandAttemptProb: 0.07,
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IslandSeedChance: 0.0025,
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MinIslandSize: 8,
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MaxIslandSize: 800,
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WaterLevelBias: 0.02,
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NoiseFrequency: 0.02,
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KeepInnerFraction: 0.85, // keep central 85% of radius
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MaxWorkers: 0,
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MinWidthPx: minWidthPx,
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MaxWidthPx: maxWidthPx,
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}
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bounds := canvas.Bounds()
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imgW, imgH := bounds.Dx(), bounds.Dy()
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// Precompute normalized height grid for faster sampling.
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heightGrid := precomputeHeightGrid(heightmap, imgW, imgH)
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// Compute bounding box for path expanded by radius + edge band
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radius := riverWidthPx / 2.0
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edgeBand := radius * params.EdgeBandRatio
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expand := int(math.Ceil(radius + edgeBand + 2))
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minX, minY := imgW, imgH
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maxX, maxY := 0, 0
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for _, p := range path {
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if p.X < minX {
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minX = p.X
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}
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if p.Y < minY {
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minY = p.Y
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}
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if p.X > maxX {
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maxX = p.X
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}
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if p.Y > maxY {
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maxY = p.Y
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}
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}
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minX -= expand
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minY -= expand
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maxX += expand
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maxY += expand
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if minX < 0 {
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minX = 0
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}
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if minY < 0 {
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minY = 0
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}
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if maxX >= imgW {
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maxX = imgW - 1
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}
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if maxY >= imgH {
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maxY = imgH - 1
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}
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bw := maxX - minX + 1
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bh := maxY - minY + 1
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if bw <= 0 || bh <= 0 {
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return nil
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}
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// Create base raster mask inside bounding box.
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// baseMask[i] == 1 means inside nominal river radius (before roughening).
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baseMask := make([]uint8, bw*bh)
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// Rasterize simple circular stamping for each center point into baseMask
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radiusSq := radius * radius
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for _, c := range path {
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cx := c.X - minX
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cy := c.Y - minY
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if cx < -int(radius) || cx > bw+int(radius) || cy < -int(radius) || cy > bh+int(radius) {
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continue
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}
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minRx := int(math.Max(0, float64(cx)-radius))
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maxRx := int(math.Min(float64(bw-1), float64(cx)+radius))
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minRy := int(math.Max(0, float64(cy)-radius))
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maxRy := int(math.Min(float64(bh-1), float64(cy)+radius))
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for yy := minRy; yy <= maxRy; yy++ {
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for xx := minRx; xx <= maxRx; xx++ {
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dx := float64(xx - cx)
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dy := float64(yy - cy)
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if dx*dx+dy*dy <= radiusSq {
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baseMask[yy*bw+xx] = 1
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}
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}
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}
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}
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// Compute distance field (approximate Euclidean) from centerline (distance 0 at pixels inside baseMask)
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dist := chamferDistanceField(baseMask, bw, bh)
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// Prepare noise generator
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noise := opensimplex.New(seed)
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noiseFreq := params.NoiseFrequency
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// Determine inner keep radius (always keep central channel)
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innerKeepRadius := radius * params.KeepInnerFraction
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// Prepare final mask
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finalMask := make([]uint8, bw*bh)
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// Concurrency setup
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workers := params.MaxWorkers
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if workers <= 0 {
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workers = runtime.NumCPU()
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}
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var wg sync.WaitGroup
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rowsPerWorker := (bh + workers - 1) / workers
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randBase := rand.New(rand.NewSource(seed))
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// Precompute some weights for the decision formula
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heightWeight := 2.0 * params.RoughnessStrength
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distWeight := params.RoughnessStrength
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noiseWeight := 0.5 * params.RoughnessStrength
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// Compute sin wave amplitudes for realistic edge roughening
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// Large amplitude is the difference between max and min river widths
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// Small amplitude is a quarter of the large amplitude for subtle bank details
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largeAmplitude := params.MaxWidthPx - params.MinWidthPx
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smallAmplitude := largeAmplitude / 4.0
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// Evaluate per-pixel decision in parallel
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for wi := 0; wi < workers; wi++ {
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startY := wi * rowsPerWorker
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endY := startY + rowsPerWorker
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if endY > bh {
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endY = bh
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}
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if startY >= endY {
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continue
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}
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wg.Add(1)
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go func(startY, endY, workerID int) {
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defer wg.Done()
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localRand := rand.New(rand.NewSource(randBase.Int63() + int64(workerID)*7919))
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for y := startY; y < endY; y++ {
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for x := 0; x < bw; x++ {
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idx := y*bw + x
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// If already inside base mask, candidate for water
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if baseMask[idx] == 1 {
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// If within inner keep radius: keep always
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d := dist[idx]
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// dist is approximate pixels; we compare to innerKeepRadius
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absX := x + minX
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absY := y + minY
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if d <= float32(innerKeepRadius) {
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finalMask[idx] = 1
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continue
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}
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// Apply sin wave offset for realistic edge roughening
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sinWaveOffset := computeSinWaveEdgeOffset(absX, absY, largeAmplitude, smallAmplitude)
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effectiveInnerRadius := innerKeepRadius + sinWaveOffset
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// Compute influences
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// normalizedDist: 0 at effectiveInnerRadius, 1 at effectiveInnerRadius + edgeBand
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normDist := float64((float32(d) - float32(effectiveInnerRadius)) / float32(edgeBand))
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if normDist < 0 {
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normDist = 0
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}
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if normDist > 1 {
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normDist = 1
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}
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heightVal := sampleHeightGrid(heightGrid, imgW, imgH, absX, absY) // 0..1
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// Apply bias so slightly lower areas favor water
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heightAdj := float64(heightVal) - params.WaterLevelBias
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noiseVal := noise.Eval2(float64(absX)*noiseFreq, float64(absY)*noiseFreq) // -1 .. 1
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noiseNorm := (noiseVal + 1.0) / 2.0 // 0..1
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score := distWeight*normDist + heightWeight*heightAdj + noiseWeight*(noiseNorm-0.5)
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// Decision threshold: higher score means more likely land.
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threshold := 0.35 + 0.5*params.RoughnessStrength
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// Small stochastic factor to add natural variance
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if localRand.Float64() < 0.0005 {
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score += (localRand.Float64() - 0.5) * 0.2
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}
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if score < threshold {
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finalMask[idx] = 1
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} else {
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finalMask[idx] = 0
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}
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}
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}
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}
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}(startY, endY, wi)
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}
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wg.Wait()
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// Optionally attempt islands with small probability
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randForIsland := rand.New(rand.NewSource(seed + 1234567))
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tryIslands := randForIsland.Float64() < params.IslandAttemptProb
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if tryIslands {
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generateIslandsInMask(finalMask, bw, bh, minX, minY, heightGrid, imgW, imgH, ¶ms, seed+4242)
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}
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// Paint finalMask to canvas and collect pixels (only those not already water)
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var added []image.Point
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for y := 0; y < bh; y++ {
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absY := y + minY
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for x := 0; x < bw; x++ {
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absX := x + minX
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pt := image.Point{X: absX, Y: absY}
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if !pt.In(bounds) {
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continue
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}
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idx := y*bw + x
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if finalMask[idx] == 1 && !isWater[pt] {
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canvas.Set(absX, absY, color.RGBA{R: 0, G: 0, B: 255, A: 255})
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isWater[pt] = true
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added = append(added, pt)
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}
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}
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}
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// Small cleanup: remove tiny isolated water pixels (optional - lightweight)
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removeSpeckles(&finalMask, bw, bh, 2)
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return added
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}
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// precomputeHeightGrid converts the heightmap to a float32 grid [0..1] sized width*height.
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func precomputeHeightGrid(hmap image.Image, width, height int) []float32 {
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out := make([]float32, width*height)
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if hmap == nil {
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// default flat
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for i := range out {
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out[i] = 0.5
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}
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return out
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}
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b := hmap.Bounds()
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for y := 0; y < height; y++ {
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for x := 0; x < width; x++ {
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absX := x + b.Min.X
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absY := y + b.Min.Y
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r, _, _, _ := hmap.At(absX, absY).RGBA()
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val := float32(r) / 65535.0
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out[y*width+x] = val
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}
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}
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return out
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}
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// sampleHeightGrid safe accessor
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func sampleHeightGrid(grid []float32, width, height, x, y int) float32 {
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if x < 0 || x >= width || y < 0 || y >= height {
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return 0.5
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}
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return grid[y*width+x]
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}
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// chamferDistanceField computes a fast approximate distance (in pixels) from any pixel to the nearest
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// baseMask==1 pixel. Distance is zero for pixels inside baseMask.
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// This is a two-pass chamfer approximation (float), cheap and parallel friendly.
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func chamferDistanceField(baseMask []uint8, w, h int) []float32 {
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const maxF = 1e6
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dist := make([]float32, w*h)
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// Initialize
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for i := 0; i < w*h; i++ {
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if baseMask[i] == 1 {
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dist[i] = 0
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} else {
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dist[i] = maxF
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}
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}
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// Forward pass
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for y := 0; y < h; y++ {
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for x := 0; x < w; x++ {
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i := y*w + x
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if dist[i] == 0 {
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continue
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}
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// check left
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if x > 0 {
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v := dist[i-1] + 1.0
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check top
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if y > 0 {
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v := dist[i-w] + 1.0
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check top-left
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if x > 0 && y > 0 {
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v := dist[i-w-1] + 1.41421356
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check top-right
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if x < w-1 && y > 0 {
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v := dist[i-w+1] + 1.41421356
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if v < dist[i] {
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dist[i] = v
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}
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}
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}
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}
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// Backward pass
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for y := h - 1; y >= 0; y-- {
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for x := w - 1; x >= 0; x-- {
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i := y*w + x
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// check right
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if x < w-1 {
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v := dist[i+1] + 1.0
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check bottom
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if y < h-1 {
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v := dist[i+w] + 1.0
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check bottom-right
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if x < w-1 && y < h-1 {
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v := dist[i+w+1] + 1.41421356
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if v < dist[i] {
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dist[i] = v
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}
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}
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// check bottom-left
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if x > 0 && y < h-1 {
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v := dist[i+w-1] + 1.41421356
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if v < dist[i] {
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dist[i] = v
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}
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}
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}
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}
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return dist
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}
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// generateIslandsInMask will attempt to create small islands inside contiguous water areas.
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// It modifies the mask in place (1=water, 0=land). The algorithm:
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// - choose candidate water pixels with slightly higher-than-water height
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// - use a small BFS flood constrained by height to form island patches
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// - reject patches that touch the bounding box edge (we want enclosed islands)
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// - enforce size limits
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func generateIslandsInMask(mask []uint8, bw, bh, minX, minY int, heightGrid []float32, fullW, fullH int, params *riverParams, seed int64) {
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r := rand.New(rand.NewSource(seed))
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// Collect candidates
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type pt struct{ x, y int }
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candidates := make([]pt, 0)
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for y := 0; y < bh; y++ {
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for x := 0; x < bw; x++ {
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idx := y*bw + x
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if mask[idx] != 1 {
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continue
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}
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absX := x + minX
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absY := y + minY
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hv := sampleHeightGrid(heightGrid, fullW, fullH, absX, absY)
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// candidate if slightly higher than local water bias
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if float64(hv) > params.WaterLevelBias+0.03 {
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if r.Float64() < params.IslandSeedChance {
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candidates = append(candidates, pt{x, y})
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}
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}
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}
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}
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if len(candidates) == 0 {
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||||
return
|
||||
}
|
||||
|
||||
// Shuffle candidates to randomize island placement
|
||||
r.Shuffle(len(candidates), func(i, j int) { candidates[i], candidates[j] = candidates[j], candidates[i] })
|
||||
|
||||
visited := make([]uint8, bw*bh)
|
||||
|
||||
for _, c := range candidates {
|
||||
ci := c.y*bw + c.x
|
||||
if visited[ci] != 0 {
|
||||
continue
|
||||
}
|
||||
// BFS grow island
|
||||
maxSize := params.MaxIslandSize
|
||||
minSize := params.MinIslandSize
|
||||
// randomize size a bit
|
||||
targetSize := minSize + r.Intn(maxSize-minSize+1)
|
||||
|
||||
queue := []pt{{c.x, c.y}}
|
||||
visited[ci] = 1
|
||||
island := make([]pt, 0, targetSize)
|
||||
touchesEdge := false
|
||||
|
||||
for qi := 0; qi < len(queue) && len(island) < targetSize; qi++ {
|
||||
p := queue[qi]
|
||||
absX := p.x + minX
|
||||
absY := p.y + minY
|
||||
// Height constraint: island must be above a modest threshold
|
||||
hv := sampleHeightGrid(heightGrid, fullW, fullH, absX, absY)
|
||||
if float64(hv) < params.WaterLevelBias+0.01 {
|
||||
continue
|
||||
}
|
||||
island = append(island, p)
|
||||
// Expand
|
||||
for dy := -1; dy <= 1; dy++ {
|
||||
for dx := -1; dx <= 1; dx++ {
|
||||
nx, ny := p.x+dx, p.y+dy
|
||||
if nx < 0 || nx >= bw || ny < 0 || ny >= bh {
|
||||
touchesEdge = true
|
||||
continue
|
||||
}
|
||||
nidx := ny*bw + nx
|
||||
if visited[nidx] != 0 {
|
||||
continue
|
||||
}
|
||||
// Only grow into water pixels
|
||||
if mask[nidx] != 1 {
|
||||
continue
|
||||
}
|
||||
visited[nidx] = 1
|
||||
queue = append(queue, pt{nx, ny})
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// If island touches bbox edge, reject it (we want enclosed islands)
|
||||
if touchesEdge {
|
||||
continue
|
||||
}
|
||||
|
||||
// size check
|
||||
if len(island) < minSize {
|
||||
continue
|
||||
}
|
||||
|
||||
// Carve the island: set mask pixels to 0 (land)
|
||||
for _, p := range island {
|
||||
mask[p.y*bw+p.x] = 0
|
||||
}
|
||||
|
||||
// Optionally stop after creating a few islands to keep them rare
|
||||
if r.Float64() < 0.7 {
|
||||
// keep creating more sometimes, break otherwise
|
||||
if r.Intn(3) == 0 {
|
||||
break
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// removeSpeckles removes tiny isolated water components (erodes islands smaller than threshold).
|
||||
// This is a simple pass that clears pixels that have fewer than minNeighbors water neighbors.
|
||||
func removeSpeckles(mask *[]uint8, bw, bh, minNeighbors int) {
|
||||
arr := *mask
|
||||
out := make([]uint8, len(arr))
|
||||
copy(out, arr)
|
||||
for y := 0; y < bh; y++ {
|
||||
for x := 0; x < bw; x++ {
|
||||
idx := y*bw + x
|
||||
if arr[idx] == 0 {
|
||||
continue
|
||||
}
|
||||
count := 0
|
||||
for dy := -1; dy <= 1; dy++ {
|
||||
for dx := -1; dx <= 1; dx++ {
|
||||
if dx == 0 && dy == 0 {
|
||||
continue
|
||||
}
|
||||
nx := x + dx
|
||||
ny := y + dy
|
||||
if nx < 0 || nx >= bw || ny < 0 || ny >= bh {
|
||||
continue
|
||||
}
|
||||
if arr[ny*bw+nx] == 1 {
|
||||
count++
|
||||
}
|
||||
}
|
||||
}
|
||||
if count < minNeighbors {
|
||||
out[idx] = 0
|
||||
}
|
||||
}
|
||||
}
|
||||
copy(arr, out)
|
||||
*mask = arr
|
||||
}
|
||||
|
||||
// (Optional) utility used for debug or visualization - not used directly in pipeline.
|
||||
func maskToPoints(mask []uint8, bw, bh, minX, minY int) []image.Point {
|
||||
var pts []image.Point
|
||||
for y := 0; y < bh; y++ {
|
||||
for x := 0; x < bw; x++ {
|
||||
if mask[y*bw+x] == 1 {
|
||||
pts = append(pts, image.Point{X: x + minX, Y: y + minY})
|
||||
}
|
||||
}
|
||||
}
|
||||
return pts
|
||||
}
|
||||
|
||||
// small clamp helpers
|
||||
func clamp01(v float64) float64 {
|
||||
if v < 0 {
|
||||
return 0
|
||||
}
|
||||
if v > 1 {
|
||||
return 1
|
||||
}
|
||||
return v
|
||||
}
|
||||
Reference in New Issue
Block a user