From 232594bee4c889d4d32161e58924d160f87724fe Mon Sep 17 00:00:00 2001
From: Subv <subv2112@gmail.com>
Date: Wed, 2 Dec 2015 13:23:51 -0500
Subject: [PATCH] Pica/Scissor: Implemented the scissor test in the sw
 renderer.

---
 src/video_core/pica.cpp       |  1 +
 src/video_core/pica.h         | 32 +++++++++++++++++++++++++++++++-
 src/video_core/rasterizer.cpp | 22 +++++++++++++++++++++-
 3 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/src/video_core/pica.cpp b/src/video_core/pica.cpp
index 8c528989e..2822a3035 100644
--- a/src/video_core/pica.cpp
+++ b/src/video_core/pica.cpp
@@ -28,6 +28,7 @@ std::string Regs::GetCommandName(int index) {
         ADD_FIELD(viewport_size_y);
         ADD_FIELD(viewport_depth_range);
         ADD_FIELD(viewport_depth_far_plane);
+        ADD_FIELD(scissor_test);
         ADD_FIELD(viewport_corner);
         ADD_FIELD(texture0_enable);
         ADD_FIELD(texture0);
diff --git a/src/video_core/pica.h b/src/video_core/pica.h
index 2f1b2dec4..6fc8b1bc5 100644
--- a/src/video_core/pica.h
+++ b/src/video_core/pica.h
@@ -112,7 +112,36 @@ struct Regs {
         BitField<24, 5, Semantic> map_w;
     } vs_output_attributes[7];
 
-    INSERT_PADDING_WORDS(0x11);
+    INSERT_PADDING_WORDS(0xe);
+
+    enum class ScissorMode : u32 {
+        Disabled = 0,
+        Exclude = 1, // Exclude pixels inside the scissor box
+
+        Include = 3 // Exclude pixels outside the scissor box
+    };
+
+    struct {
+        BitField<0, 2, ScissorMode> mode;
+
+        union {
+            BitField< 0, 16, u32> right;
+            BitField<16, 16, u32> bottom;
+        };
+
+        union {
+            BitField< 0, 16, u32> left;
+            BitField<16, 16, u32> top;
+        };
+
+        u32 GetWidth() const {
+            return left - right + 1;
+        }
+
+        u32 GetHeight() const {
+            return top - bottom + 1;
+        }
+    } scissor_test;
 
     union {
         BitField< 0, 16, u32> x;
@@ -986,6 +1015,7 @@ ASSERT_REG_POSITION(viewport_depth_range, 0x4d);
 ASSERT_REG_POSITION(viewport_depth_far_plane, 0x4e);
 ASSERT_REG_POSITION(vs_output_attributes[0], 0x50);
 ASSERT_REG_POSITION(vs_output_attributes[1], 0x51);
+ASSERT_REG_POSITION(scissor_test, 0x65);
 ASSERT_REG_POSITION(viewport_corner, 0x68);
 ASSERT_REG_POSITION(texture0_enable, 0x80);
 ASSERT_REG_POSITION(texture0, 0x81);
diff --git a/src/video_core/rasterizer.cpp b/src/video_core/rasterizer.cpp
index ecfdbc9e8..4249ae235 100644
--- a/src/video_core/rasterizer.cpp
+++ b/src/video_core/rasterizer.cpp
@@ -334,12 +334,25 @@ static void ProcessTriangleInternal(const Shader::OutputVertex& v0,
             return;
     }
 
-    // TODO: Proper scissor rect test!
     u16 min_x = std::min({vtxpos[0].x, vtxpos[1].x, vtxpos[2].x});
     u16 min_y = std::min({vtxpos[0].y, vtxpos[1].y, vtxpos[2].y});
     u16 max_x = std::max({vtxpos[0].x, vtxpos[1].x, vtxpos[2].x});
     u16 max_y = std::max({vtxpos[0].y, vtxpos[1].y, vtxpos[2].y});
 
+    // Convert the scissor box coordinates to 12.4 fixed point
+    u16 scissor_width = (u16)(regs.scissor_test.GetWidth() << 4);
+    u16 scissor_height = (u16)(regs.scissor_test.GetHeight() << 4);
+    u16 scissor_x = (u16)(regs.scissor_test.right << 4);
+    u16 scissor_y = (u16)(regs.scissor_test.bottom << 4);
+
+    if (regs.scissor_test.mode == Regs::ScissorMode::Include) {
+        // Calculate the new bounds
+        min_x = std::max(min_x, scissor_x);
+        min_y = std::max(min_y, scissor_y);
+        max_x = std::min(max_x, (u16)(scissor_x + scissor_width));
+        max_y = std::min(max_y, (u16)(scissor_y + scissor_height));
+    }
+
     min_x &= Fix12P4::IntMask();
     min_y &= Fix12P4::IntMask();
     max_x = ((max_x + Fix12P4::FracMask()) & Fix12P4::IntMask());
@@ -379,6 +392,13 @@ static void ProcessTriangleInternal(const Shader::OutputVertex& v0,
     for (u16 y = min_y + 8; y < max_y; y += 0x10) {
         for (u16 x = min_x + 8; x < max_x; x += 0x10) {
 
+            // Do not process the pixel if it's inside the scissor box and the scissor mode is set to Exclude
+            if (regs.scissor_test.mode == Regs::ScissorMode::Exclude) {
+                if (x >= scissor_x && x <= scissor_x + scissor_width &&
+                    y >= scissor_y && y <= scissor_y + scissor_height)
+                    continue;
+            }
+
             // Calculate the barycentric coordinates w0, w1 and w2
             int w0 = bias0 + SignedArea(vtxpos[1].xy(), vtxpos[2].xy(), {x, y});
             int w1 = bias1 + SignedArea(vtxpos[2].xy(), vtxpos[0].xy(), {x, y});