Pica/Rasterizer: Make orient2d a free function and rename it to SignedArea.

src/video_core/rasterizer.cpp

@@ -55,12 +55,8 @@ static void SetDepth(int x, int y, u16 value) {
     *(depth_buffer + x + y * registers.framebuffer.GetWidth()) = value;
 }
 
-void ProcessTriangle(const VertexShader::OutputVertex& v0,
+// NOTE: Assuming that rasterizer coordinates are 12.4 fixed-point values
-                     const VertexShader::OutputVertex& v1,
+struct Fix12P4 {
-                     const VertexShader::OutputVertex& v2)
-{
-    // NOTE: Assuming that rasterizer coordinates are 12.4 fixed-point values
-    struct Fix12P4 {
     Fix12P4() {}
     Fix12P4(u16 val) : val(val) {}
 
@@ -75,24 +71,35 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
         return (u16)*this < (u16)oth;
     }
 
-    private:
+private:
     u16 val;
-    };
+};
 
-    // vertex positions in rasterizer coordinates
+/**
-    auto FloatToFix = [](float24 flt) {
+ * Calculate signed area of the triangle spanned by the three argument vertices.
-                          return Fix12P4(static_cast<unsigned short>(flt.ToFloat32() * 16.0f));
+ * The sign denotes an orientation.
-                      };
+ *
-    auto ScreenToRasterizerCoordinates = [FloatToFix](const Math::Vec3<float24> vec) {
+ * @todo define orientation concretely.
-                                             return Math::Vec3<Fix12P4>{FloatToFix(vec.x), FloatToFix(vec.y), FloatToFix(vec.z)};
+ */
-                                         };
+static int SignedArea (const Math::Vec2<Fix12P4>& vtx1,
-    static auto orient2d = [](const Math::Vec2<Fix12P4>& vtx1,
                        const Math::Vec2<Fix12P4>& vtx2,
                        const Math::Vec2<Fix12P4>& vtx3) {
     const auto vec1 = Math::MakeVec(vtx2 - vtx1, 0);
     const auto vec2 = Math::MakeVec(vtx3 - vtx1, 0);
     // TODO: There is a very small chance this will overflow for sizeof(int) == 4
     return Math::Cross(vec1, vec2).z;
+};
+
+void ProcessTriangle(const VertexShader::OutputVertex& v0,
+                     const VertexShader::OutputVertex& v1,
+                     const VertexShader::OutputVertex& v2)
+{
+    // vertex positions in rasterizer coordinates
+    auto FloatToFix = [](float24 flt) {
+                          return Fix12P4(static_cast<unsigned short>(flt.ToFloat32() * 16.0f));
+                      };
+    auto ScreenToRasterizerCoordinates = [FloatToFix](const Math::Vec3<float24> vec) {
+                                             return Math::Vec3<Fix12P4>{FloatToFix(vec.x), FloatToFix(vec.y), FloatToFix(vec.z)};
                                          };
 
     Math::Vec3<Fix12P4> vtxpos[3]{ ScreenToRasterizerCoordinates(v0.screenpos),
@@ -107,7 +114,7 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
     if (registers.cull_mode != Regs::CullMode::KeepAll) {
         // Cull away triangles which are wound clockwise.
         // TODO: A check for degenerate triangles ("== 0") should be considered for CullMode::KeepAll
-        if (orient2d(vtxpos[0].xy(), vtxpos[1].xy(), vtxpos[2].xy()) <= 0)
+        if (SignedArea(vtxpos[0].xy(), vtxpos[1].xy(), vtxpos[2].xy()) <= 0)
             return;
     }
 
@@ -153,9 +160,9 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
         for (u16 x = min_x; x < max_x; x += 0x10) {
 
             // Calculate the barycentric coordinates w0, w1 and w2
-            int w0 = bias0 + orient2d(vtxpos[1].xy(), vtxpos[2].xy(), {x, y});
+            int w0 = bias0 + SignedArea(vtxpos[1].xy(), vtxpos[2].xy(), {x, y});
-            int w1 = bias1 + orient2d(vtxpos[2].xy(), vtxpos[0].xy(), {x, y});
+            int w1 = bias1 + SignedArea(vtxpos[2].xy(), vtxpos[0].xy(), {x, y});
-            int w2 = bias2 + orient2d(vtxpos[0].xy(), vtxpos[1].xy(), {x, y});
+            int w2 = bias2 + SignedArea(vtxpos[0].xy(), vtxpos[1].xy(), {x, y});
             int wsum = w0 + w1 + w2;
 
             // If current pixel is not covered by the current primitive