GLState: Support changing the GL_TEXTURE_SWIZZLE parameter of each texture unit.

src/video_core/renderer_opengl/gl_state.cpp

@@ -50,6 +50,10 @@ OpenGLState::OpenGLState() {
     for (auto& texture_unit : texture_units) {
         texture_unit.texture_2d = 0;
         texture_unit.sampler = 0;
+        texture_unit.swizzle.r = GL_RED;
+        texture_unit.swizzle.g = GL_GREEN;
+        texture_unit.swizzle.b = GL_BLUE;
+        texture_unit.swizzle.a = GL_ALPHA;
     }
 
     lighting_lut.texture_buffer = 0;
@@ -200,6 +204,15 @@ void OpenGLState::Apply() const {
         if (texture_units[i].sampler != cur_state.texture_units[i].sampler) {
             glBindSampler(i, texture_units[i].sampler);
         }
+        // Update the texture swizzle
+        if (texture_units[i].swizzle.r != cur_state.texture_units[i].swizzle.r ||
+            texture_units[i].swizzle.g != cur_state.texture_units[i].swizzle.g ||
+            texture_units[i].swizzle.b != cur_state.texture_units[i].swizzle.b ||
+            texture_units[i].swizzle.a != cur_state.texture_units[i].swizzle.a) {
+            std::array<GLint, 4> mask = {texture_units[i].swizzle.r, texture_units[i].swizzle.g,
+                                         texture_units[i].swizzle.b, texture_units[i].swizzle.a};
+            glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_RGBA, mask.data());
+        }
     }
 
     // Constbuffers

src/video_core/renderer_opengl/gl_state.h

@@ -85,6 +85,12 @@ public:
     struct {
         GLuint texture_2d; // GL_TEXTURE_BINDING_2D
         GLuint sampler;    // GL_SAMPLER_BINDING
+        struct {
+            GLint r; // GL_TEXTURE_SWIZZLE_R
+            GLint g; // GL_TEXTURE_SWIZZLE_G
+            GLint b; // GL_TEXTURE_SWIZZLE_B
+            GLint a; // GL_TEXTURE_SWIZZLE_A
+        } swizzle;
     } texture_units[32];
 
     struct {

src/video_core/renderer_opengl/renderer_opengl.cpp

@@ -316,6 +316,7 @@ void RendererOpenGL::DrawScreenTriangles(const ScreenInfo& screen_info, float x,
     }};
 
     state.texture_units[0].texture_2d = screen_info.display_texture;
+    state.texture_units[0].swizzle = {GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA};
     state.Apply();
 
     glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices.data());