LUT interpolation

apps/LoopThroughWithOpenGLCompositing/gl/TextureAssetLoader.cpp

@@ -4,12 +4,120 @@
 #include <wincodec.h>
 
 #include <atlbase.h>
+#include <algorithm>
+#include <cctype>
 #include <cstring>
+#include <fstream>
+#include <sstream>
+#include <string>
 #include <vector>
 
+#ifndef GL_RGBA32F
+#define GL_RGBA32F 0x8814
+#endif
+
+namespace
+{
+std::string LowercaseExtension(const std::filesystem::path& path)
+{
+	std::string extension = path.extension().string();
+	std::transform(extension.begin(), extension.end(), extension.begin(),
+		[](unsigned char value) { return static_cast<char>(std::tolower(value)); });
+	return extension;
+}
+
+bool LoadCubeTextureAsset(const ShaderTextureAsset& textureAsset, GLuint& textureId, std::string& error)
+{
+	std::ifstream file(textureAsset.path);
+	if (!file)
+	{
+		error = "Could not open shader LUT asset: " + textureAsset.path.string();
+		return false;
+	}
+
+	unsigned lutSize = 0;
+	std::vector<float> values;
+	std::string line;
+	while (std::getline(file, line))
+	{
+		const std::size_t commentStart = line.find('#');
+		if (commentStart != std::string::npos)
+			line.resize(commentStart);
+
+		std::istringstream stream(line);
+		std::string firstToken;
+		if (!(stream >> firstToken))
+			continue;
+
+		if (firstToken == "TITLE" || firstToken == "DOMAIN_MIN" || firstToken == "DOMAIN_MAX")
+			continue;
+		if (firstToken == "LUT_3D_SIZE")
+		{
+			stream >> lutSize;
+			continue;
+		}
+		if (firstToken == "LUT_1D_SIZE")
+		{
+			error = "Only 3D .cube LUT assets are supported: " + textureAsset.path.string();
+			return false;
+		}
+
+		float red = 0.0f;
+		float green = 0.0f;
+		float blue = 0.0f;
+		try
+		{
+			red = std::stof(firstToken);
+		}
+		catch (...)
+		{
+			error = "Unsupported .cube directive in shader LUT asset: " + firstToken;
+			return false;
+		}
+		if (!(stream >> green >> blue))
+		{
+			error = "Malformed RGB entry in shader LUT asset: " + textureAsset.path.string();
+			return false;
+		}
+		values.push_back(red);
+		values.push_back(green);
+		values.push_back(blue);
+		values.push_back(1.0f);
+	}
+
+	if (lutSize == 0)
+	{
+		error = "Shader LUT asset is missing LUT_3D_SIZE: " + textureAsset.path.string();
+		return false;
+	}
+
+	const std::size_t expectedFloats = static_cast<std::size_t>(lutSize) * lutSize * lutSize * 4;
+	if (values.size() != expectedFloats)
+	{
+		error = "Shader LUT asset entry count does not match LUT_3D_SIZE: " + textureAsset.path.string();
+		return false;
+	}
+
+	const GLsizei atlasWidth = static_cast<GLsizei>(lutSize * lutSize);
+	const GLsizei atlasHeight = static_cast<GLsizei>(lutSize);
+	glGenTextures(1, &textureId);
+	glBindTexture(GL_TEXTURE_2D, textureId);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+	glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
+	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, atlasWidth, atlasHeight, 0, GL_RGBA, GL_FLOAT, values.data());
+	glBindTexture(GL_TEXTURE_2D, 0);
+	return true;
+}
+}
+
 bool LoadTextureAsset(const ShaderTextureAsset& textureAsset, GLuint& textureId, std::string& error)
 {
 	textureId = 0;
+	if (LowercaseExtension(textureAsset.path) == ".cube")
+		return LoadCubeTextureAsset(textureAsset, textureId, error);
 
 	HRESULT comInitResult = CoInitializeEx(NULL, COINIT_MULTITHREADED);
 	const bool shouldUninitializeCom = (comInitResult == S_OK || comInitResult == S_FALSE);