random float

README.md

@@ -245,4 +245,3 @@ If `SLANG_ROOT` is not set, the workflow falls back to the repo-local default un
 - allow shaders to read other shaders data store based on name? or putput over OSC
 - Mipmappong needed?
 - unwrap a fish eyelens and mirror it and map it to equirectangulr for environmnet map purposes
-- add a random flaot between 0-1 that changes each time the application loads for shaders to use

SHADER_CONTRACT.md

@@ -76,7 +76,7 @@ Important rules:
 - Keep parameter IDs, texture IDs, font IDs, and function entry points as valid shader identifiers: letters, numbers, and underscores only, starting with a letter or underscore.
 - Add only controls that are actually used by the shader.
 - Prefer a small number of clear controls with conservative defaults.
-- Keep shaders deterministic unless randomness is an explicit feature. For stable pseudo-randomness, hash from `uv`, pixel coordinates, `frameCount`, or trigger values rather than using unavailable global state.
+- Keep shaders deterministic unless randomness is an explicit feature. For stable process-level variation, use `context.startupRandom`; for per-pixel pseudo-randomness, hash from `uv`, pixel coordinates, `frameCount`, or trigger values.
 - If adapting third-party code, include attribution and source URL in the manifest description when the license allows adaptation.
 - If the source license is unclear or incompatible, do not add the shader package.
 
@@ -149,6 +149,7 @@ struct ShaderContext
     float time;
     float utcTimeSeconds;
     float utcOffsetSeconds;
+    float startupRandom;
     float frameCount;
     float mixAmount;
     float bypass;
@@ -166,6 +167,7 @@ Fields:
 - `time`: elapsed runtime time in seconds.
 - `utcTimeSeconds`: current UTC time of day from the host PC clock, expressed as seconds since UTC midnight.
 - `utcOffsetSeconds`: host PC local UTC offset in seconds. Add this to `utcTimeSeconds` and wrap to `0..86400` to get local time of day.
+- `startupRandom`: random `0..1` value generated once when the host process starts. It stays constant for the lifetime of the app and changes on the next launch.
 - `frameCount`: incrementing frame counter.
 - `mixAmount`: runtime mix amount.
 - `bypass`: `1.0` when the layer is bypassed, otherwise `0.0`.

apps/LoopThroughWithOpenGLCompositing/gl/GlobalParamsBuffer.cpp

@@ -20,6 +20,7 @@ bool GlobalParamsBuffer::Update(const RuntimeRenderState& state, unsigned availa
 	AppendStd140Vec2(buffer, static_cast<float>(state.outputWidth), static_cast<float>(state.outputHeight));
 	AppendStd140Float(buffer, static_cast<float>(state.utcTimeSeconds));
 	AppendStd140Float(buffer, static_cast<float>(state.utcOffsetSeconds));
+	AppendStd140Float(buffer, static_cast<float>(state.startupRandom));
 	AppendStd140Float(buffer, static_cast<float>(state.frameCount));
 	AppendStd140Float(buffer, static_cast<float>(state.mixAmount));
 	AppendStd140Float(buffer, static_cast<float>(state.bypass));

apps/LoopThroughWithOpenGLCompositing/runtime/RuntimeHost.cpp

@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <cmath>
 #include <fstream>
+#include <random>
 #include <set>
 #include <sstream>
 
@@ -55,6 +56,13 @@ bool MatchesControlKey(const std::string& candidate, const std::string& key)
 	return candidate == key || SimplifyControlKey(candidate) == SimplifyControlKey(key);
 }
 
+double GenerateStartupRandom()
+{
+	std::random_device randomDevice;
+	std::uniform_real_distribution<double> distribution(0.0, 1.0);
+	return distribution(randomDevice);
+}
+
 bool TryParseLayerIdNumber(const std::string& layerId, uint64_t& number)
 {
 	const std::string prefix = "layer-";
@@ -691,6 +699,7 @@ RuntimeHost::RuntimeHost()
 	mCompletionIntervalMilliseconds(0.0),
 	mSmoothedCompletionIntervalMilliseconds(0.0),
 	mMaxCompletionIntervalMilliseconds(0.0),
+	mStartupRandom(GenerateStartupRandom()),
 	mLateFrameCount(0),
 	mDroppedFrameCount(0),
 	mFlushedFrameCount(0),
@@ -1351,6 +1360,7 @@ void RuntimeHost::RefreshDynamicRenderStateFields(std::vector<RuntimeRenderState
 		state.timeSeconds = timeSeconds;
 		state.utcTimeSeconds = clock.utcTimeSeconds;
 		state.utcOffsetSeconds = clock.utcOffsetSeconds;
+		state.startupRandom = mStartupRandom;
 		state.frameCount = frameCount;
 	}
 }

apps/LoopThroughWithOpenGLCompositing/runtime/RuntimeHost.h

@@ -167,6 +167,7 @@ private:
 	double mCompletionIntervalMilliseconds;
 	double mSmoothedCompletionIntervalMilliseconds;
 	double mMaxCompletionIntervalMilliseconds;
+	double mStartupRandom;
 	uint64_t mLateFrameCount;
 	uint64_t mDroppedFrameCount;
 	uint64_t mFlushedFrameCount;

apps/LoopThroughWithOpenGLCompositing/shader/ShaderTypes.h

@@ -115,6 +115,7 @@ struct RuntimeRenderState
 	double timeSeconds = 0.0;
 	double utcTimeSeconds = 0.0;
 	double utcOffsetSeconds = 0.0;
+	double startupRandom = 0.0;
 	double frameCount = 0.0;
 	double mixAmount = 1.0;
 	double bypass = 0.0;

runtime/templates/shader_wrapper.slang.in

@@ -13,6 +13,7 @@ struct ShaderContext
 	float time;
 	float utcTimeSeconds;
 	float utcOffsetSeconds;
+	float startupRandom;
 	float frameCount;
 	float mixAmount;
 	float bypass;
@@ -27,6 +28,7 @@ cbuffer GlobalParams
 	float2 gOutputResolution;
 	float gUtcTimeSeconds;
 	float gUtcOffsetSeconds;
+	float gStartupRandom;
 	float gFrameCount;
 	float gMixAmount;
 	float gBypass;
@@ -86,6 +88,7 @@ float4 fragmentMain(FragmentInput input) : SV_Target
 	context.time = gTime;
 	context.utcTimeSeconds = gUtcTimeSeconds;
 	context.utcOffsetSeconds = gUtcOffsetSeconds;
+	context.startupRandom = gStartupRandom;
 	context.frameCount = gFrameCount;
 	context.mixAmount = gMixAmount;
 	context.bypass = gBypass;

tests/Std140BufferTests.cpp

@@ -64,6 +64,7 @@ void TestGlobalParamStylePacking()
 	AppendStd140Vec2(buffer, 1280.0f, 720.0f);		// output resolution
 	AppendStd140Float(buffer, 45296.0f);			// UTC time of day
 	AppendStd140Float(buffer, 36000.0f);			// UTC offset
+	AppendStd140Float(buffer, 0.75f);				// startup random
 	AppendStd140Float(buffer, 42.0f);				// frame count
 	AppendStd140Float(buffer, 0.5f);				// mix
 	AppendStd140Float(buffer, 1.0f);				// bypass
@@ -76,17 +77,18 @@ void TestGlobalParamStylePacking()
 	AppendStd140Int(buffer, 2);						// enum parameter
 	buffer.resize(AlignStd140(buffer.size(), 16), 0);
 
-	Expect(buffer.size() == 96, "global parameter style block is padded to a 16-byte boundary");
+	Expect(buffer.size() == 112, "global parameter style block is padded to a 16-byte boundary");
 	Expect(ReadFloat(buffer, 0) == 10.0f, "time is at the start of the block");
 	Expect(ReadFloat(buffer, 8) == 1920.0f, "first vec2 aligns after scalar padding");
 	Expect(ReadFloat(buffer, 16) == 1280.0f, "second vec2 follows first vec2");
 	Expect(ReadFloat(buffer, 24) == 45296.0f, "UTC time follows output resolution");
 	Expect(ReadFloat(buffer, 28) == 36000.0f, "UTC offset follows UTC time");
-	Expect(ReadInt(buffer, 44) == 3, "history length scalar remains tightly packed");
+	Expect(ReadFloat(buffer, 32) == 0.75f, "startup random follows UTC offset");
-	Expect(ReadFloat(buffer, 56) == 4.0f, "vec2 shader parameter aligns to 8 bytes");
+	Expect(ReadInt(buffer, 48) == 3, "history length scalar remains tightly packed");
-	Expect(ReadFloat(buffer, 64) == 0.1f, "color parameter aligns to 16 bytes");
+	Expect(ReadFloat(buffer, 64) == 4.0f, "vec2 shader parameter aligns to 8 bytes");
-	Expect(ReadInt(buffer, 80) == 1, "boolean parameter follows vec4");
+	Expect(ReadFloat(buffer, 80) == 0.1f, "color parameter aligns to 16 bytes");
-	Expect(ReadInt(buffer, 84) == 2, "enum parameter follows boolean");
+	Expect(ReadInt(buffer, 96) == 1, "boolean parameter follows vec4");
+	Expect(ReadInt(buffer, 100) == 2, "enum parameter follows boolean");
 }
 }