Pica/Rasterizer: Implement backface culling.
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3b78af904e
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0f49424022
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@ -50,7 +50,19 @@ struct Regs {
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u32 trigger_irq;
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INSERT_PADDING_WORDS(0x30);
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INSERT_PADDING_WORDS(0x2f);
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enum class CullMode : u32 {
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// Select which polygons are considered to be "frontfacing".
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KeepAll = 0,
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KeepClockWise = 1,
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KeepCounterClockWise = 2,
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// TODO: What does the third value imply?
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};
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union {
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BitField<0, 2, CullMode> cull_mode;
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};
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BitField<0, 24, u32> viewport_size_x;
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@ -659,6 +671,7 @@ struct Regs {
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} while(false)
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ADD_FIELD(trigger_irq);
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ADD_FIELD(cull_mode);
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ADD_FIELD(viewport_size_x);
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ADD_FIELD(viewport_size_y);
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ADD_FIELD(viewport_depth_range);
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@ -730,6 +743,7 @@ private:
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#define ASSERT_REG_POSITION(field_name, position) static_assert(offsetof(Regs, field_name) == position * 4, "Field "#field_name" has invalid position")
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ASSERT_REG_POSITION(trigger_irq, 0x10);
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ASSERT_REG_POSITION(cull_mode, 0x40);
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ASSERT_REG_POSITION(viewport_size_x, 0x41);
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ASSERT_REG_POSITION(viewport_size_y, 0x43);
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ASSERT_REG_POSITION(viewport_depth_range, 0x4d);
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@ -82,10 +82,31 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
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auto ScreenToRasterizerCoordinates = [FloatToFix](const Math::Vec3<float24> vec) {
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return Math::Vec3<Fix12P4>{FloatToFix(vec.x), FloatToFix(vec.y), FloatToFix(vec.z)};
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};
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static auto orient2d = [](const Math::Vec2<Fix12P4>& vtx1,
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const Math::Vec2<Fix12P4>& vtx2,
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const Math::Vec2<Fix12P4>& vtx3) {
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const auto vec1 = Math::MakeVec(vtx2 - vtx1, 0);
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const auto vec2 = Math::MakeVec(vtx3 - vtx1, 0);
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// TODO: There is a very small chance this will overflow for sizeof(int) == 4
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return Math::Cross(vec1, vec2).z;
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};
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Math::Vec3<Fix12P4> vtxpos[3]{ ScreenToRasterizerCoordinates(v0.screenpos),
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ScreenToRasterizerCoordinates(v1.screenpos),
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ScreenToRasterizerCoordinates(v2.screenpos) };
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if (registers.cull_mode == Regs::CullMode::KeepClockWise) {
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// Reverse vertex order and use the CCW code path.
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std::swap(vtxpos[1], vtxpos[2]);
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}
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if (registers.cull_mode != Regs::CullMode::KeepAll) {
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// Cull away triangles which are wound clockwise.
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// TODO: A check for degenerate triangles ("== 0") should be considered for CullMode::KeepAll
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if (orient2d(vtxpos[0].xy(), vtxpos[1].xy(), vtxpos[2].xy()) <= 0)
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return;
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}
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// TODO: Proper scissor rect test!
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u16 min_x = std::min({vtxpos[0].x, vtxpos[1].x, vtxpos[2].x});
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u16 min_y = std::min({vtxpos[0].y, vtxpos[1].y, vtxpos[2].y});
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@ -128,15 +149,6 @@ void ProcessTriangle(const VertexShader::OutputVertex& v0,
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for (u16 x = min_x; x < max_x; x += 0x10) {
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// Calculate the barycentric coordinates w0, w1 and w2
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auto orient2d = [](const Math::Vec2<Fix12P4>& vtx1,
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const Math::Vec2<Fix12P4>& vtx2,
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const Math::Vec2<Fix12P4>& vtx3) {
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const auto vec1 = Math::MakeVec(vtx2 - vtx1, 0);
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const auto vec2 = Math::MakeVec(vtx3 - vtx1, 0);
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// TODO: There is a very small chance this will overflow for sizeof(int) == 4
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return Math::Cross(vec1, vec2).z;
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};
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int w0 = bias0 + orient2d(vtxpos[1].xy(), vtxpos[2].xy(), {x, y});
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int w1 = bias1 + orient2d(vtxpos[2].xy(), vtxpos[0].xy(), {x, y});
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int w2 = bias2 + orient2d(vtxpos[0].xy(), vtxpos[1].xy(), {x, y});
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