1 files changed, 190 insertions, 0 deletions
diff --git a/third_party/rust/wpf-gpu-raster/src/tri_rasterize.rs b/third_party/rust/wpf-gpu-raster/src/tri_rasterize.rs
new file mode 100644
index 0000000000..28fbf6a73f
--- /dev/null
+++ b/third_party/rust/wpf-gpu-raster/src/tri_rasterize.rs
@@ -0,0 +1,190 @@
+/* The rasterization code here is based off of piglit/tests/general/triangle-rasterization.cpp:
+
+    /**************************************************************************
+     *
+     * Copyright 2012 VMware, Inc.
+     * All Rights Reserved.
+     *
+     * Permission is hereby granted, free of charge, to any person obtaining a
+     * copy of this software and associated documentation files (the
+     * "Software"), to deal in the Software without restriction, including
+     * without limitation the rights to use, copy, modify, merge, publish,
+     * distribute, sub license, and/or sell copies of the Software, and to
+     * permit persons to whom the Software is furnished to do so, subject to
+     * the following conditions:
+     *
+     * The above copyright notice and this permission notice (including the
+     * next paragraph) shall be included in all copies or substantial portions
+     * of the Software.
+     *
+     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+     * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+     * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
+     * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
+     * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+     * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+     * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+     *
+     **************************************************************************/
+
+*/
+
+use std::ops::Index;
+use crate::OutputVertex;
+#[derive(Debug)]
+struct Vertex {
+    x: f32,
+    y: f32,
+    coverage: f32
+}
+#[derive(Debug)]
+struct Triangle {
+    v: [Vertex; 3],
+}
+
+impl Index<usize> for Triangle  {
+    type Output = Vertex;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.v[index]
+    }
+}
+
+// D3D11 mandates 8 bit subpixel precision:
+// https://microsoft.github.io/DirectX-Specs/d3d/archive/D3D11_3_FunctionalSpec.htm#CoordinateSnapping
+const FIXED_SHIFT: i32 = 8;
+const FIXED_ONE: f32 = (1 << FIXED_SHIFT) as f32;
+
+/* Proper rounding of float to integer */
+fn iround(mut v: f32) -> i64 {
+    if v > 0.0 {
+        v += 0.5;
+    }
+    if v < 0.0 {
+        v -= 0.5;
+    }
+    return v as i64
+}
+
+/* Based on http://devmaster.net/forums/topic/1145-advanced-rasterization */
+fn rast_triangle(buffer: &mut [u8], width: usize, height: usize, tri: &Triangle) {
+    let center_offset = -0.5;
+
+    let mut coverage1 = tri[0].coverage;
+    let mut coverage2 = tri[1].coverage;
+    let mut coverage3 = tri[2].coverage;
+
+    /* fixed point coordinates */
+    let mut x1 = iround(FIXED_ONE * (tri[0].x + center_offset));
+    let     x2 = iround(FIXED_ONE * (tri[1].x + center_offset));
+    let mut x3 = iround(FIXED_ONE * (tri[2].x + center_offset));
+
+    let mut y1 = iround(FIXED_ONE * (tri[0].y + center_offset));
+    let     y2 = iround(FIXED_ONE * (tri[1].y + center_offset));
+    let mut y3 = iround(FIXED_ONE * (tri[2].y + center_offset));
+
+
+    /* Force correct vertex order */
+    let cross = (x2 - x1) * (y3 - y2) - (y2 - y1) * (x3 - x2);
+    if cross > 0 {
+        std::mem::swap(&mut x1, &mut x3);
+        std::mem::swap(&mut y1, &mut y3);
+        // I don't understand why coverage 2 and 3 are swapped instead of 1 and 3
+        std::mem::swap(&mut coverage2, &mut coverage3);
+    } else {
+        std::mem::swap(&mut coverage1, &mut coverage3);
+    }
+
+    /* Deltas */
+    let dx12 = x1 - x2;
+    let dx23 = x2 - x3;
+    let dx31 = x3 - x1;
+
+    let dy12 = y1 - y2;
+    let dy23 = y2 - y3;
+    let dy31 = y3 - y1;
+
+    /* Fixed-point deltas */
+    let fdx12 = dx12 << FIXED_SHIFT;
+    let fdx23 = dx23 << FIXED_SHIFT;
+    let fdx31 = dx31 << FIXED_SHIFT;
+
+    let fdy12 = dy12 << FIXED_SHIFT;
+    let fdy23 = dy23 << FIXED_SHIFT;
+    let fdy31 = dy31 << FIXED_SHIFT;
+
+    /* Bounding rectangle */
+    let mut minx = x1.min(x2).min(x3) >> FIXED_SHIFT;
+    let mut maxx = x1.max(x2).max(x3) >> FIXED_SHIFT;
+
+    let mut miny = y1.min(y2).min(y3) >> FIXED_SHIFT;
+    let mut maxy = y1.max(y2).max(y3) >> FIXED_SHIFT;
+
+    minx = minx.max(0);
+    maxx = maxx.min(width as i64 - 1);
+
+    miny = miny.max(0);
+    maxy = maxy.min(height as i64 - 1);
+
+    /* Half-edge constants */
+    let mut c1 = dy12 * x1 - dx12 * y1;
+    let mut c2 = dy23 * x2 - dx23 * y2;
+    let mut c3 = dy31 * x3 - dx31 * y3;
+
+    /* Correct for top-left filling convention */
+    if dy12 < 0 || (dy12 == 0 && dx12 < 0) { c1 += 1 }
+    if dy23 < 0 || (dy23 == 0 && dx23 < 0) { c2 += 1 }
+    if dy31 < 0 || (dy31 == 0 && dx31 < 0) { c3 += 1 }
+
+    let mut cy1 = c1 + dx12 * (miny << FIXED_SHIFT) - dy12 * (minx << FIXED_SHIFT);
+    let mut cy2 = c2 + dx23 * (miny << FIXED_SHIFT) - dy23 * (minx << FIXED_SHIFT);
+    let mut cy3 = c3 + dx31 * (miny << FIXED_SHIFT) - dy31 * (minx << FIXED_SHIFT);
+    //dbg!(minx, maxx, tri, cross);
+    /* Perform rasterization */
+    let mut buffer = &mut buffer[miny as usize * width..];
+    for _y in miny..=maxy {
+        let mut cx1 = cy1;
+        let mut cx2 = cy2;
+        let mut cx3 = cy3;
+
+        for x in minx..=maxx {
+            if cx1 > 0 && cx2 > 0 && cx3 > 0 {
+                // cross is equal to 2*area of the triangle.
+                // we can normalize cx by 2*area to get barycentric coords.
+                let area = cross.abs() as f32;
+                let bary = (cx1 as f32 / area, cx2 as f32 / area, cx3 as f32 / area);
+                let coverages = coverage1 * bary.0 + coverage2 * bary.1 + coverage3 * bary.2;
+                let color = (coverages * 255. + 0.5) as u8;
+
+                buffer[x as usize] = color;
+            }
+
+            cx1 -= fdy12;
+            cx2 -= fdy23;
+            cx3 -= fdy31;
+        }
+
+        cy1 += fdx12;
+        cy2 += fdx23;
+        cy3 += fdx31;
+
+        buffer = &mut buffer[width..];
+    }
+}
+
+pub fn rasterize_to_mask(vertices: &[OutputVertex], width: u32, height: u32) -> Box<[u8]> {
+    let mut mask = vec![0; (width * height) as usize];
+    for n in (0..vertices.len()).step_by(3) {
+        let tri =
+            [&vertices[n], &vertices[n+1], &vertices[n+2]];
+
+        let tri = Triangle { v: [
+            Vertex { x: tri[0].x, y: tri[0].y, coverage: tri[0].coverage},
+            Vertex { x: tri[1].x, y: tri[1].y, coverage: tri[1].coverage},
+            Vertex { x: tri[2].x, y: tri[2].y, coverage: tri[2].coverage}
+            ]
+        };
+        rast_triangle(&mut mask, width as usize, height as usize, &tri);
+    }
+    mask.into_boxed_slice()
+}