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/* 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::Vertex as 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()
}
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