GPU/OpenGL: Use shader instead of framebuffer blit

src/core/shadergen.cpp

@@ -617,3 +617,19 @@ std::string ShaderGen::GenerateCopyFragmentShader()
 
   return ss.str();
 }
+
+std::string ShaderGen::GenerateSampleFragmentShader()
+{
+  std::stringstream ss;
+  WriteHeader(ss);
+  DeclareTexture(ss, "samp0", 0);
+  DeclareFragmentEntryPoint(ss, 0, 1, {}, false, 1);
+
+  ss << R"(
+{
+  o_col0 = SAMPLE_TEXTURE(samp0, v_tex0);
+}
+)";
+
+  return ss.str();
+}