OPENGL: Support GLSL based CLUT8 look up for GLES2+.

6 files changed, 14 insertions, 19 deletions

diff --git a/backends/graphics/opengl/context.cpp b/backends/graphics/opengl/context.cpp
index c149b12f19..89f0ed7910 100644
--- a/backends/graphics/opengl/context.cpp
+++ b/backends/graphics/opengl/context.cpp
@@ -36,7 +36,6 @@ void Context::reset() {
 	shadersSupported = false;
 	multitextureSupported = false;
 	framebufferObjectSupported = false;
-	textureRGSupported = false;
 
 #define GL_FUNC_DEF(ret, name, param) name = nullptr;
 #include "backends/graphics/opengl/opengl-func.h"
@@ -206,8 +205,6 @@ void OpenGLGraphicsManager::initializeGLContext() {
 			ARBFragmentShader = true;
 		} else if (token == "GL_ARB_multitexture") {
 			g_context.multitextureSupported = true;
-		} else if (token == "GL_ARB_texture_rg") {
-			g_context.textureRGSupported = true;
 		} else if (token == "GL_EXT_framebuffer_object") {
 			g_context.framebufferObjectSupported = true;
 		}
@@ -248,7 +245,6 @@ void OpenGLGraphicsManager::initializeGLContext() {
 	debug(5, "OpenGL: NPOT texture support: %d", g_context.NPOTSupported);
 	debug(5, "OpenGL: Shader support: %d", g_context.shadersSupported);
 	debug(5, "OpenGL: Multitexture support: %d", g_context.multitextureSupported);
-	debug(5, "OpenGL: Texture RG support: %d", g_context.textureRGSupported);
 	debug(5, "OpenGL: FBO support: %d", g_context.framebufferObjectSupported);
 }
 
diff --git a/backends/graphics/opengl/opengl-func.h b/backends/graphics/opengl/opengl-func.h
index 763d5e9143..554ac3c6ff 100644
--- a/backends/graphics/opengl/opengl-func.h
+++ b/backends/graphics/opengl/opengl-func.h
@@ -130,13 +130,11 @@ GL_FUNC_2_DEF(void, glGetShaderInfoLog, glGetInfoLogARB, (GLshader shader, GLsiz
 GL_FUNC_2_DEF(void, glShaderSource, glShaderSourceARB, (GLshader shader, GLsizei count, const GLchar *const *string, const GLint *length));
 GL_FUNC_2_DEF(void, glCompileShader, glCompileShaderARB, (GLshader shader));
 
-#if !USE_FORCED_GLES2
 GL_FUNC_2_DEF(void, glBindFramebuffer, glBindFramebufferEXT, (GLenum target, GLuint renderbuffer));
 GL_FUNC_2_DEF(void, glDeleteFramebuffers, glDeleteFramebuffersEXT, (GLsizei n, const GLuint *framebuffers));
 GL_FUNC_2_DEF(void, glGenFramebuffers, glGenFramebuffersEXT, (GLsizei n, GLuint *renderbuffers));
 GL_FUNC_2_DEF(void, glFramebufferTexture2D, glFramebufferTexture2DEXT, (GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level));
 GL_FUNC_2_DEF(GLenum, glCheckFramebufferStatus, glCheckFramebufferStatusEXT, (GLenum target));
-#endif
 
 GL_FUNC_2_DEF(void, glActiveTexture, glActiveTextureARB, (GLenum texture));
 #endif
diff --git a/backends/graphics/opengl/opengl-graphics.cpp b/backends/graphics/opengl/opengl-graphics.cpp
index d9c9377e51..1ec40015af 100644
--- a/backends/graphics/opengl/opengl-graphics.cpp
+++ b/backends/graphics/opengl/opengl-graphics.cpp
@@ -1016,7 +1016,7 @@ void OpenGLGraphicsManager::setMousePosition(int x, int y) {
 Surface *OpenGLGraphicsManager::createSurface(const Graphics::PixelFormat &format, bool wantAlpha) {
 	GLenum glIntFormat, glFormat, glType;
 	if (format.bytesPerPixel == 1) {
-#if !USE_FORCED_GLES && !USE_FORCED_GLES2
+#if !USE_FORCED_GLES
 		if (TextureCLUT8GPU::isSupportedByContext()) {
 			return new TextureCLUT8GPU();
 		}
diff --git a/backends/graphics/opengl/opengl-sys.h b/backends/graphics/opengl/opengl-sys.h
index 9c3dfe8244..a584259abe 100644
--- a/backends/graphics/opengl/opengl-sys.h
+++ b/backends/graphics/opengl/opengl-sys.h
@@ -114,9 +114,6 @@ struct Context {
 	/** Whether multi texture support is available or not. */
 	bool multitextureSupported;
 
-	/** Whether (GLES2) RG texture formats are supported. */
-	bool textureRGSupported;
-
 	/** Whether FBO support is available or not. */
 	bool framebufferObjectSupported;
 
diff --git a/backends/graphics/opengl/texture.cpp b/backends/graphics/opengl/texture.cpp
index 5ae4987874..f98bf8be06 100644
--- a/backends/graphics/opengl/texture.cpp
+++ b/backends/graphics/opengl/texture.cpp
@@ -504,9 +504,9 @@ void TextureRGB555::updateTexture() {
 }
 #endif // !USE_FORCED_GL
 
-#if !USE_FORCED_GLES && !USE_FORCED_GLES2
+#if !USE_FORCED_GLES
 namespace {
-const char *const g_lookUpFragmentShaderGL =
+const char *const g_lookUpFragmentShader =
 	"varying vec2 texCoord;\n"
 	"varying vec4 blendColor;\n"
 	"\n"
@@ -517,12 +517,17 @@ const char *const g_lookUpFragmentShaderGL =
 	"\n"
 	"void main(void) {\n"
 	"\tvec4 index = texture2D(texture, texCoord);\n"
-	"\tgl_FragColor = blendColor * texture2D(palette, vec2(index.x * adjustFactor, 0.0));\n"
+	"\tgl_FragColor = blendColor * texture2D(palette, vec2(index.a * adjustFactor, 0.0));\n"
 	"}\n";
 } // End of anonymous namespace
 
+// _clut8Texture needs 8 bits internal precision, otherwise graphics glitches
+// can occur. GL_ALPHA does not have any internal precision requirements.
+// However, in practice (according to fuzzie) it's 8bit. If we run into
+// problems, we need to switch to GL_R8 and GL_RED, but that is only supported
+// for ARB_texture_rg and GLES3+ (EXT_rexture_rg does not support GL_R8).
 TextureCLUT8GPU::TextureCLUT8GPU()
-    : _clut8Texture(GL_R8, GL_RED, GL_UNSIGNED_BYTE),
+    : _clut8Texture(GL_ALPHA, GL_ALPHA, GL_UNSIGNED_BYTE),
       _paletteTexture(GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE),
       _glTexture(GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE),
       _glFBO(0), _clut8Vertices(), _projectionMatrix(),
@@ -531,7 +536,7 @@ TextureCLUT8GPU::TextureCLUT8GPU()
 	// Allocate space for 256 colors.
 	_paletteTexture.setSize(256, 1);
 
-	_lookUpShader = new Shader(g_defaultVertexShader, g_lookUpFragmentShaderGL);
+	_lookUpShader = new Shader(g_defaultVertexShader, g_lookUpFragmentShader);
 	_lookUpShader->recreate();
 	_paletteLocation = _lookUpShader->getUniformLocation("palette");
 
@@ -772,6 +777,6 @@ void TextureCLUT8GPU::setupFBO() {
 	// Restore old FBO.
 	GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, oldFBO));
 }
-#endif // !USE_FORCED_GLES && !USE_FORCED_GLES2
+#endif // !USE_FORCED_GLES
 
 } // End of namespace OpenGL
diff --git a/backends/graphics/opengl/texture.h b/backends/graphics/opengl/texture.h
index 06fe47a241..959281539f 100644
--- a/backends/graphics/opengl/texture.h
+++ b/backends/graphics/opengl/texture.h
@@ -317,7 +317,7 @@ private:
 };
 #endif // !USE_FORCED_GL
 
-#if !USE_FORCED_GLES && !USE_FORCED_GLES2
+#if !USE_FORCED_GLES
 class TextureCLUT8GPU : public Surface {
 public:
 	TextureCLUT8GPU();
@@ -351,7 +351,6 @@ public:
 	static bool isSupportedByContext() {
 		return g_context.shadersSupported
 		    && g_context.multitextureSupported
-		    && g_context.textureRGSupported
 		    && g_context.framebufferObjectSupported;
 	}
 private:
@@ -376,7 +375,7 @@ private:
 	byte _palette[4 * 256];
 	bool _paletteDirty;
 };
-#endif // !USE_FORCED_GLES && !USE_FORCED_GLES2
+#endif // !USE_FORCED_GLES
 
 } // End of namespace OpenGL