Freeing up a rain pass channel

shaders/glsl/rainPass.compute.frag.glsl

@@ -3,7 +3,7 @@ precision highp float;
 // This shader is the star of the show. For each glyph, it determines its:
 // 		R: brightness
 // 		G: progress through the glyph sequence
-// 		B: depth, aka distance from the screen
+// 		B: unused!
 // 		A: additional brightness for effects
 
 // Listen.
@@ -24,7 +24,7 @@ uniform bool hasSun, hasThunder, loops;
 uniform bool showComputationTexture;
 uniform float brightnessOverride, brightnessThreshold, brightnessDecay;
 uniform float baseContrast, baseBrightness;
-uniform float raindropLength, glyphHeightToWidth;
+uniform float raindropLength, glyphHeightToWidth, glyphSequenceLength;
 uniform int cycleStyle, rippleType;
 uniform float rippleScale, rippleSpeed, rippleThickness;
 uniform float cursorEffectThreshold;
@@ -188,10 +188,7 @@ vec4 computeResult(bool isFirstFrame, vec4 previousResult, vec2 glyphPos, vec2 s
 		brightness = mix(previousBrightness, brightness, brightnessDecay);
 	}
 
-	// Determine the glyph depth. This is a static value for each column.
-	float depth = randomFloat(vec2(screenPos.x, 0.));
-
-	vec4 result = vec4(brightness, cycle, depth, effect);
+	vec4 result = vec4(brightness, cycle, 0.0, effect);
 
 	// Better use of the alpha channel, for demonstrating how the glyph cycle works
 	if (showComputationTexture) {

shaders/glsl/rainPass.frag.glsl

@@ -18,15 +18,21 @@ uniform bool volumetric;
 varying vec2 vUV;
 varying vec3 vChannel;
 varying vec4 vGlyph;
+varying float vDepth;
 
 float median3(vec3 i) {
 	return max(min(i.r, i.g), min(max(i.r, i.g), i.b));
 }
 
+float modI(float a, float b) {
+	float m = a - floor((a + 0.5) / b) * b;
+	return floor(m + 0.5);
+}
+
 vec2 getSymbolUV(float glyphCycle) {
-	float symbol = floor((glyphSequenceLength) * glyphCycle) + 1.0;
-	float symbolX = mod(symbol, glyphTextureGridSize.x);
-	float symbolY = mod(floor(symbol / glyphTextureGridSize.x), glyphTextureGridSize.y);
+	float symbol = floor((glyphSequenceLength) * glyphCycle);
+	float symbolX = modI(symbol, glyphTextureGridSize.x);
+	float symbolY = (symbol - symbolX) / glyphTextureGridSize.x;
 	symbolY = glyphTextureGridSize.y - symbolY - 1.0;
 	return vec2(symbolX, symbolY);
 }
@@ -59,13 +65,12 @@ void main() {
 	vec4 glyph = volumetric ? vGlyph : texture2D(state, uv);
 	float brightness = glyph.r;
 	vec2 symbolUV = getSymbolUV(glyph.g);
-	float quadDepth = glyph.b;
 	float effect = glyph.a;
 
 	brightness = max(effect, brightness);
 	// In volumetric mode, distant glyphs are dimmer
 	if (volumetric) {
-		brightness = brightness * min(1.0, quadDepth);
+		brightness = brightness * min(1.0, vDepth);
 	}
 
 	// resolve UV to cropped position of glyph in MSDF texture

shaders/glsl/rainPass.vert.glsl

@@ -12,6 +12,7 @@ uniform bool volumetric;
 varying vec2 vUV;
 varying vec3 vChannel;
 varying vec4 vGlyph;
+varying float vDepth;
 
 highp float rand( const in vec2 uv ) {
 	const highp float a = 12.9898, b = 78.233, c = 43758.5453;
@@ -27,8 +28,9 @@ void main() {
 	// Calculate the world space position
 	float quadDepth = 0.0;
 	if (volumetric) {
-		quadDepth = fract(vGlyph.b + time * animationSpeed * forwardSpeed);
-		vGlyph.b = quadDepth;
+		float startDepth = rand(vec2(aPosition.x, 0.));
+		quadDepth = fract(startDepth + time * animationSpeed * forwardSpeed);
+		vDepth = quadDepth;
 	}
 	vec2 position = (aPosition * vec2(1., glyphVerticalSpacing) + aCorner * vec2(density, 1.)) * quadSize;
 	vec4 pos = vec4((position - 0.5) * 2.0, quadDepth, 1.0);