renderer_opengl: Swizzle BGR textures on copy

OpenGL does not natively support BGR internal formats, which causes many BGR textures to render incorrectly, with Red and Blue channels swapped.

This commit aims to address this by swizzling the blue and red channels on texture copies when a BGR format is encountered.

src/video_core/host_shaders/CMakeLists.txt

@@ -5,6 +5,7 @@ set(SHADER_FILES
     convert_float_to_depth.frag
     full_screen_triangle.vert
     opengl_copy_bc4.comp
+    opengl_copy_bgra.comp
     opengl_present.frag
     opengl_present.vert
     pitch_unswizzle.comp

src/video_core/host_shaders/opengl_copy_bgra.comp

@@ -0,0 +1,15 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#version 430 core
+
+layout (local_size_x = 4, local_size_y = 4) in;
+
+layout(binding = 0, rgba8) readonly uniform image2DArray bgr_input;
+layout(binding = 1, rgba8) writeonly uniform image2DArray bgr_output;
+
+void main() {
+    vec4 color = imageLoad(bgr_input, ivec3(gl_GlobalInvocationID));
+    imageStore(bgr_output, ivec3(gl_GlobalInvocationID), color.bgra);
+}