Add more blend equations from 3dbrew

src/video_core/pica.h

@@ -338,7 +338,11 @@ struct Regs {
 
         union {
             enum BlendEquation : u32 {
-                Add = 0,
+                Add             = 0,
+                Subtract        = 1,
+                ReverseSubtract = 2,
+                Min             = 3,
+                Max             = 4
             };
 
             enum BlendFactor : u32 {

src/video_core/rasterizer.cpp

@@ -616,17 +616,60 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
                                                LookupFactorA(params.factor_source_a));
                 auto dstfactor = Math::MakeVec(LookupFactorRGB(params.factor_dest_rgb),
                                                LookupFactorA(params.factor_dest_a));
+                                               
+                auto src_result = (combiner_output * srcfactor).Cast<int>();
+                auto dst_result = (dest * dstfactor).Cast<int>();
 
                 switch (params.blend_equation_rgb) {
                 case params.Add:
                 {
-                    auto result = (combiner_output * srcfactor + dest * dstfactor) / 255;
+                    auto result = (src_result + dst_result) / 255;
                     result.r() = std::min(255, result.r());
                     result.g() = std::min(255, result.g());
                     result.b() = std::min(255, result.b());
                     combiner_output = result.Cast<u8>();
                     break;
                 }
+                
+                case params.Subtract:
+                {
+                    auto result = (src_result - dst_result) / 255;
+                    result.r() = std::max(0, result.r());
+                    result.g() = std::max(0, result.g());
+                    result.b() = std::max(0, result.b());
+                    combiner_output = result.Cast<u8>();
+                    break;
+                }
+                
+                case params.ReverseSubtract:
+                {
+                    auto result = (dst_result - src_result) / 255;
+                    result.r() = std::max(0, result.r());
+                    result.g() = std::max(0, result.g());
+                    result.b() = std::max(0, result.b());
+                    combiner_output = result.Cast<u8>();
+                    break;
+                }
+                
+                case params.Min:
+                {
+                    Math::Vec4<int> result;
+                    result.r() = std::min(src_result.r(),dst_result.r());
+                    result.g() = std::min(src_result.g(),dst_result.g());
+                    result.b() = std::min(src_result.b(),dst_result.b());
+                    combiner_output = result.Cast<u8>();
+                    break;
+                }
+                
+                case params.Max:
+                {
+                    Math::Vec4<int> result;
+                    result.r() = std::max(src_result.r(),dst_result.r());
+                    result.g() = std::max(src_result.g(),dst_result.g());
+                    result.b() = std::max(src_result.b(),dst_result.b());
+                    combiner_output = result.Cast<u8>();
+                    break;
+                }
 
                 default:
                     LOG_CRITICAL(HW_GPU, "Unknown RGB blend equation %x", params.blend_equation_rgb.Value());