Adding intro and skipIntro option

shaders/glsl/rainPass.frag.glsl

@@ -61,7 +61,7 @@ vec2 getUV(vec2 uv) {
 
 vec3 getBrightness(vec4 raindrop, vec4 effect, float quadDepth, vec2 uv) {
 
-	float base = raindrop.r;
+	float base = raindrop.r + max(0., 1.0 - raindrop.a * 5.0);
 	bool isCursor = bool(raindrop.g) && isolateCursor;
 	float glint = base;
 	float multipliedEffects = effect.r;
@@ -94,7 +94,7 @@ vec3 getBrightness(vec4 raindrop, vec4 effect, float quadDepth, vec2 uv) {
 	return vec3(
 		(isCursor ? vec2(0.0, 1.0) : vec2(1.0, 0.0)) * base,
 		glint
-	);
+	) * raindrop.b;
 }
 
 vec2 getSymbolUV(float index) {

shaders/glsl/rainPass.intro.frag.glsl

@@ -0,0 +1,59 @@
+precision highp float;
+
+// This shader governs the "intro"— the initial stream of rain from a blank screen.
+// It writes falling rain to the channels of a data texture:
+// 		R: raindrop length
+// 		G: unused
+// 		B: unused
+// 		A: unused
+
+#define PI 3.14159265359
+#define SQRT_2 1.4142135623730951
+#define SQRT_5 2.23606797749979
+
+uniform sampler2D previousIntroState;
+uniform float numColumns, numRows;
+uniform float time, tick;
+uniform float animationSpeed, fallSpeed;
+
+uniform bool skipIntro;
+
+// Helper functions for generating randomness, borrowed from elsewhere
+
+highp float randomFloat( const in vec2 uv ) {
+	const highp float a = 12.9898, b = 78.233, c = 43758.5453;
+	highp float dt = dot( uv.xy, vec2( a,b ) ), sn = mod( dt, PI );
+	return fract(sin(sn) * c);
+}
+
+vec2 randomVec2( const in vec2 uv ) {
+	return fract(vec2(sin(uv.x * 591.32 + uv.y * 154.077), cos(uv.x * 391.32 + uv.y * 49.077)));
+}
+
+float wobble(float x) {
+	return x + 0.3 * sin(SQRT_2 * x) + 0.2 * sin(SQRT_5 * x);
+}
+
+// Main function
+
+vec4 computeResult(float simTime, bool isFirstFrame, vec2 glyphPos, vec2 screenPos, vec4 previous) {
+	if (skipIntro) {
+		return vec4(1., 0., 0., 0.);
+	}
+
+	float columnTimeOffset = randomFloat(vec2(glyphPos.x, 0.)) * -10.;
+	columnTimeOffset += sin(glyphPos.x / numColumns * PI) - 1.;
+	float introTime = (simTime + columnTimeOffset) * fallSpeed / numRows * 100.;
+
+	vec4 result = vec4(introTime, 0., 0., 0.);
+	return result;
+}
+
+void main()	{
+	float simTime = time * animationSpeed;
+	bool isFirstFrame = tick <= 1.;
+	vec2 glyphPos = gl_FragCoord.xy;
+	vec2 screenPos = glyphPos / vec2(numColumns, numRows);
+	vec4 previous = texture2D( previousIntroState, screenPos );
+	gl_FragColor = computeResult(simTime, isFirstFrame, glyphPos, screenPos, previous);
+}

shaders/glsl/rainPass.raindrop.frag.glsl

@@ -4,7 +4,7 @@ precision highp float;
 // It writes falling rain to the channels of a data texture:
 // 		R: raindrop brightness
 // 		G: whether the cell is a "cursor"
-// 		B: unused
+// 		B: whether the cell is "activated" — to animate the intro
 // 		A: unused
 
 // Listen.
@@ -16,15 +16,14 @@ precision highp float;
 #define SQRT_2 1.4142135623730951
 #define SQRT_5 2.23606797749979
 
-uniform sampler2D previousShineState;
+uniform sampler2D previousRaindropState, introState;
 uniform float numColumns, numRows;
 uniform float time, tick;
 uniform float animationSpeed, fallSpeed;
 
-uniform bool loops;
+uniform bool loops, skipIntro;
 uniform float brightnessDecay;
-uniform float baseContrast, baseBrightness;
-uniform float raindropLength, glyphHeightToWidth;
+uniform float raindropLength;
 
 // Helper functions for generating randomness, borrowed from elsewhere
 
@@ -61,10 +60,17 @@ float getRainBrightness(float simTime, vec2 glyphPos) {
 
 // Main function
 
-vec4 computeResult(float simTime, bool isFirstFrame, vec2 glyphPos, vec2 screenPos, vec4 previous) {
+vec4 computeResult(float simTime, bool isFirstFrame, vec2 glyphPos, vec4 previous, vec4 intro) {
 	float brightness = getRainBrightness(simTime, glyphPos);
 	float brightnessBelow = getRainBrightness(simTime, glyphPos + vec2(0., -1.));
-	float cursor = brightness > brightnessBelow ? 1.0 : 0.0;
+
+	float introProgress = intro.r - (1. - glyphPos.y / numRows);
+	float introProgressBelow = intro.r - (1. - (glyphPos.y - 1.) / numRows);
+
+	bool activated = bool(previous.b) || skipIntro || introProgress > 0.;
+	bool activatedBelow = skipIntro || introProgressBelow > 0.;
+
+	bool cursor = brightness > brightnessBelow || (activated && !activatedBelow);
 
 	// Blend the glyph's brightness with its previous brightness, so it winks on and off organically
 	if (!isFirstFrame) {
@@ -72,7 +78,7 @@ vec4 computeResult(float simTime, bool isFirstFrame, vec2 glyphPos, vec2 screenP
 		brightness = mix(previousBrightness, brightness, brightnessDecay);
 	}
 
-	vec4 result = vec4(brightness, cursor, 0.0, 0.0);
+	vec4 result = vec4(brightness, cursor, activated, introProgress);
 	return result;
 }
 
@@ -81,6 +87,7 @@ void main()	{
 	bool isFirstFrame = tick <= 1.;
 	vec2 glyphPos = gl_FragCoord.xy;
 	vec2 screenPos = glyphPos / vec2(numColumns, numRows);
-	vec4 previous = texture2D( previousShineState, screenPos );
-	gl_FragColor = computeResult(simTime, isFirstFrame, glyphPos, screenPos, previous);
+	vec4 previous = texture2D( previousRaindropState, screenPos );
+	vec4 intro = texture2D( introState, vec2(screenPos.x, 0.) );
+	gl_FragColor = computeResult(simTime, isFirstFrame, glyphPos, previous, intro);
 }