Pica: Implement W-Buffer in SW rasterizer

src/video_core/clipper.cpp

@@ -75,8 +75,6 @@ static void InitScreenCoordinates(OutputVertex& vtx)
     viewport.halfsize_y = float24::FromRaw(regs.viewport_size_y);
     viewport.offset_x   = float24::FromFloat32(static_cast<float>(regs.viewport_corner.x));
     viewport.offset_y   = float24::FromFloat32(static_cast<float>(regs.viewport_corner.y));
-    viewport.zscale     = float24::FromRaw(regs.viewport_depth_range);
-    viewport.offset_z   = float24::FromRaw(regs.viewport_depth_far_plane);
 
     float24 inv_w = float24::FromFloat32(1.f) / vtx.pos.w;
     vtx.color *= inv_w;
@@ -89,7 +87,7 @@ static void InitScreenCoordinates(OutputVertex& vtx)
 
     vtx.screenpos[0] = (vtx.pos.x * inv_w + float24::FromFloat32(1.0)) * viewport.halfsize_x + viewport.offset_x;
     vtx.screenpos[1] = (vtx.pos.y * inv_w + float24::FromFloat32(1.0)) * viewport.halfsize_y + viewport.offset_y;
-    vtx.screenpos[2] = viewport.offset_z + vtx.pos.z * inv_w * viewport.zscale;
+    vtx.screenpos[2] = vtx.pos.z * inv_w;
 }
 
 void ProcessTriangle(const OutputVertex &v0, const OutputVertex &v1, const OutputVertex &v2) {

src/video_core/pica.h

@@ -70,7 +70,7 @@ struct Regs {
     INSERT_PADDING_WORDS(0x9);
 
     BitField<0, 24, u32> viewport_depth_range; // float24
-    BitField<0, 24, u32> viewport_depth_far_plane; // float24
+    BitField<0, 24, u32> viewport_depth_near_plane; // float24
 
     BitField<0, 3, u32> vs_output_total;
 
@@ -122,7 +122,20 @@ struct Regs {
         BitField<16, 10, s32> y;
     } viewport_corner;
 
-    INSERT_PADDING_WORDS(0x17);
+    INSERT_PADDING_WORDS(0x1);
+
+    //TODO: early depth
+    INSERT_PADDING_WORDS(0x1);
+
+    INSERT_PADDING_WORDS(0x2);
+
+    enum DepthBuffering : u32 {
+        WBuffering  = 0,
+        ZBuffering  = 1,
+    };
+    BitField< 0, 1, DepthBuffering> depthmap_enable;
+
+    INSERT_PADDING_WORDS(0x12);
 
     struct TextureConfig {
         enum WrapMode : u32 {
@@ -1279,10 +1292,11 @@ ASSERT_REG_POSITION(cull_mode, 0x40);
 ASSERT_REG_POSITION(viewport_size_x, 0x41);
 ASSERT_REG_POSITION(viewport_size_y, 0x43);
 ASSERT_REG_POSITION(viewport_depth_range, 0x4d);
-ASSERT_REG_POSITION(viewport_depth_far_plane, 0x4e);
+ASSERT_REG_POSITION(viewport_depth_near_plane, 0x4e);
 ASSERT_REG_POSITION(vs_output_attributes[0], 0x50);
 ASSERT_REG_POSITION(vs_output_attributes[1], 0x51);
 ASSERT_REG_POSITION(viewport_corner, 0x68);
+ASSERT_REG_POSITION(depthmap_enable, 0x6D);
 ASSERT_REG_POSITION(texture0_enable, 0x80);
 ASSERT_REG_POSITION(texture0, 0x81);
 ASSERT_REG_POSITION(texture0_format, 0x8e);

src/video_core/rasterizer.cpp

@@ -862,10 +862,30 @@ static void ProcessTriangleInternal(const Shader::OutputVertex& v0,
                 }
             }
 
+            // interpolated_z = z / w
+            float interpolated_z_over_w = (v0.screenpos[2].ToFloat32() * w0 +
+                                           v1.screenpos[2].ToFloat32() * w1 +
+                                           v2.screenpos[2].ToFloat32() * w2) / wsum;
+
+            // Not fully accurate. About 3 bits in precision are missing.
+            // Z-Buffer (z / w * scale + offset)
+            float depth_scale = float24::FromRaw(regs.viewport_depth_range).ToFloat32();
+            float depth_offset = float24::FromRaw(regs.viewport_depth_near_plane).ToFloat32();
+            float depth = interpolated_z_over_w * depth_scale + depth_offset;
+
+            // Potentially switch to W-Buffer
+            if (regs.depthmap_enable == Pica::Regs::DepthBuffering::WBuffering) {
+
+                // W-Buffer (z * scale + w * offset = (z / w * scale + offset) * w)
+                depth *= interpolated_w_inverse.ToFloat32() * wsum;
+            }
+
+            // Clamp the result
+            depth = MathUtil::Clamp(depth, 0.0f, 1.0f);
+
+            // Convert float to integer
             unsigned num_bits = Regs::DepthBitsPerPixel(regs.framebuffer.depth_format);
-            u32 z = (u32)((v0.screenpos[2].ToFloat32() * w0 +
+            u32 z = (u32)(depth * ((1 << num_bits) - 1));
-                           v1.screenpos[2].ToFloat32() * w1 +
-                           v2.screenpos[2].ToFloat32() * w2) * ((1 << num_bits) - 1) / wsum);
 
             if (output_merger.depth_test_enable) {
                 u32 ref_z = GetDepth(x >> 4, y >> 4);

src/video_core/renderer_opengl/gl_rasterizer.cpp

@@ -256,7 +256,7 @@ void RasterizerOpenGL::NotifyPicaRegisterChanged(u32 id) {
 
     // Depth modifiers
     case PICA_REG_INDEX(viewport_depth_range):
-    case PICA_REG_INDEX(viewport_depth_far_plane):
+    case PICA_REG_INDEX(viewport_depth_near_plane):
         SyncDepthModifiers();
         break;
 
@@ -911,7 +911,7 @@ void RasterizerOpenGL::SyncCullMode() {
 
 void RasterizerOpenGL::SyncDepthModifiers() {
     float depth_scale = -Pica::float24::FromRaw(Pica::g_state.regs.viewport_depth_range).ToFloat32();
-    float depth_offset = Pica::float24::FromRaw(Pica::g_state.regs.viewport_depth_far_plane).ToFloat32() / 2.0f;
+    float depth_offset = Pica::float24::FromRaw(Pica::g_state.regs.viewport_depth_near_plane).ToFloat32() / 2.0f;
 
     // TODO: Implement scale modifier
     uniform_block_data.data.depth_offset = depth_offset;