annotations

apps/LoopThroughWithOpenGLCompositing/gl/pipeline/OpenGLRenderPass.cpp

@@ -93,6 +93,9 @@ std::vector<RenderPassDescriptor> OpenGLRenderPass::BuildLayerPassDescriptors(
 	const std::vector<RuntimeRenderState>& layerStates,
 	std::vector<LayerProgram>& layerPrograms) const
 {
+	// Flatten the layer stack into concrete GL passes. A layer may now contain
+	// several shader passes, but the outer stack still sees one visible output
+	// per layer.
 	std::vector<RenderPassDescriptor> passes;
 	const std::size_t passCount = layerStates.size() < layerPrograms.size() ? layerStates.size() : layerPrograms.size();
 	std::size_t descriptorCount = 0;
@@ -108,6 +111,9 @@ std::vector<RenderPassDescriptor> OpenGLRenderPass::BuildLayerPassDescriptors(
 		LayerProgram& layerProgram = layerPrograms[index];
 		if (layerProgram.passes.empty())
 			continue;
+
+		// Preserve the original two-target layer ping-pong. Intermediate passes
+		// inside this layer are routed through pooled temporary targets instead.
 		const std::size_t remaining = layerStates.size() - index;
 		const bool writeToMain = (remaining % 2) == 1;
 		const GLuint layerOutputTexture = writeToMain ? mRenderer.CompositeTexture() : mRenderer.LayerTempTexture();
@@ -132,6 +138,8 @@ std::vector<RenderPassDescriptor> OpenGLRenderPass::BuildLayerPassDescriptors(
 			GLuint passSourceFramebuffer = previousPassFramebuffer;
 			if (!passProgram.inputNames.empty())
 			{
+				// v1 multipass uses the first declared input as gVideoInput.
+				// Later inputs are parsed for forward compatibility.
 				const std::string& inputName = passProgram.inputNames.front();
 				if (inputName == "layerInput")
 				{
@@ -159,6 +167,8 @@ std::vector<RenderPassDescriptor> OpenGLRenderPass::BuildLayerPassDescriptors(
 			RenderPassOutputTarget outputTarget = layerOutputTarget;
 			if (!writesLayerOutput)
 			{
+				// Temporary targets are reserved when the shader stack is
+				// committed, avoiding texture allocation during playback.
 				if (temporaryTargetIndex < mRenderer.TemporaryRenderTargetCount())
 				{
 					const RenderTarget& temporaryTarget = mRenderer.TemporaryRenderTarget(temporaryTargetIndex);
@@ -186,6 +196,8 @@ std::vector<RenderPassDescriptor> OpenGLRenderPass::BuildLayerPassDescriptors(
 			pass.capturePreLayerHistory = passIndex == 0 && state.temporalHistorySource == TemporalHistorySource::PreLayerInput;
 			passes.push_back(pass);
 
+			// A later pass can reference either the explicit output name or the
+			// pass id, which keeps small manifests pleasant to write.
 			namedOutputs[outputName] = std::make_pair(passDestinationTexture, passDestinationFramebuffer);
 			namedOutputs[passProgram.passId] = std::make_pair(passDestinationTexture, passDestinationFramebuffer);
 			previousPassTexture = passDestinationTexture;
@@ -253,6 +265,8 @@ void OpenGLRenderPass::RenderShaderProgram(
 	mTextureBindings.BindRuntimeTexturePlan(texturePlan);
 	glBindVertexArray(mRenderer.FullscreenVertexArray());
 	glUseProgram(passProgram.program);
+	// The UBO is shared by every pass in a layer; texture routing is what
+	// changes from pass to pass.
 	updateGlobalParams(state, mRenderer.TemporalHistory().SourceAvailableCount(), mRenderer.TemporalHistory().AvailableCountForLayer(state.layerId));
 	glDrawArrays(GL_TRIANGLES, 0, 3);
 	glUseProgram(0);