shader progress

engine/depth.go

@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"image"
 	"log"
 
 	"github.com/hajimehoshi/ebiten/v2"
@@ -9,6 +10,21 @@ import (
 const screenShaderSrc = `package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	// Image 0 is the image being drawn.
+	// Image 1 is the depth map of the image being drawn.
+	// Image 2 is the depth buffer.
+
+	// Convert the colours from the depth map and depth buffer into scalars.
+	stairs := vec4(1, 256, 65536, 16777216)
+	c1 := imageSrc1UnsafeAt(texCoord)
+	c2 := imageSrc2UnsafeAt(texCoord)
+	d1 := dot(c1, stairs)
+	d2 := dot(c2, stairs)
+
+	// If the depth buffer value is higher, return transparent.
+	if d2 > d1 {
+		return vec4(0)
+	}
 	return imageSrc0UnsafeAt(texCoord)
 }
 `
@@ -16,7 +32,21 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 const depthShaderSrc = `package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	return imageSrc0UnsafeAt(texCoord)
+	// Image 0 is the depth buffer being updated.
+	// Image 1 is the depth map being drawn from.
+
+	// Convert the colour vectors into scalars.
+	stairs := vec4(1, 256, 65536, 16777216)
+	c0 := imageSrc0UnsafeAt(texCoord)
+	c1 := imageSrc1UnsafeAt(texCoord)
+	d0 := dot(c0, stairs)
+	d1 := dot(c1, stairs)
+
+	// Write back the larger of the two.
+	if d0 > d1 {
+		return c0
+	}
+	return c1
 }
 `
 
@@ -37,5 +67,21 @@ func init() {
 }
 
 type DepthBuffer struct {
-	Buffer *ebiten.Image
+	buffer *ebiten.Image
+}
+
+func NewDepthBuffer(size image.Point) *DepthBuffer {
+	return &DepthBuffer{
+		buffer: ebiten.NewImage(size.X, size.Y),
+	}
+}
+
+func (b *DepthBuffer) Draw(dst, src, srcDepth *ebiten.Image) {
+	w, h := 0, 0
+	dst.DrawRectShader(w, h, screenShader, &ebiten.DrawRectShaderOptions{
+		Images: [4]*ebiten.Image{src, srcDepth, b.buffer},
+	})
+	dst.DrawRectShader(w, h, depthShader, &ebiten.DrawRectShaderOptions{
+		Images: [4]*ebiten.Image{b.buffer, srcDepth},
+	})
 }