tiny_skia/
blitter.rs

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1// Copyright 2006 The Android Open Source Project
2// Copyright 2020 Yevhenii Reizner
3//
4// Use of this source code is governed by a BSD-style license that can be
5// found in the LICENSE file.
6
7use crate::geom::ScreenIntRect;
8
9use crate::alpha_runs::AlphaRun;
10use crate::color::AlphaU8;
11use crate::LengthU32;
12
13/// Mask is used to describe alpha bitmaps.
14pub struct Mask {
15    pub image: [u8; 2],
16    pub bounds: ScreenIntRect,
17    pub row_bytes: u32,
18}
19
20/// Blitter is responsible for actually writing pixels into memory.
21///
22/// Besides efficiency, they handle clipping and antialiasing.
23/// An object that implements Blitter contains all the context needed to generate pixels
24/// for the destination and how src/generated pixels map to the destination.
25/// The coordinates passed to the `blit_*` calls are in destination pixel space.
26pub trait Blitter {
27    /// Blits a horizontal run of one or more pixels.
28    fn blit_h(&mut self, _x: u32, _y: u32, _width: LengthU32) {
29        unreachable!()
30    }
31
32    /// Blits a horizontal run of antialiased pixels.
33    ///
34    /// runs[] is a *sparse* zero-terminated run-length encoding of spans of constant alpha values.
35    ///
36    /// The runs[] and antialias[] work together to represent long runs of pixels with the same
37    /// alphas. The runs[] contains the number of pixels with the same alpha, and antialias[]
38    /// contain the coverage value for that number of pixels. The runs[] (and antialias[]) are
39    /// encoded in a clever way. The runs array is zero terminated, and has enough entries for
40    /// each pixel plus one, in most cases some of the entries will not contain valid data. An entry
41    /// in the runs array contains the number of pixels (np) that have the same alpha value. The
42    /// next np value is found np entries away. For example, if runs[0] = 7, then the next valid
43    /// entry will by at runs[7]. The runs array and antialias[] are coupled by index. So, if the
44    /// np entry is at runs[45] = 12 then the alpha value can be found at antialias[45] = 0x88.
45    /// This would mean to use an alpha value of 0x88 for the next 12 pixels starting at pixel 45.
46    fn blit_anti_h(
47        &mut self,
48        _x: u32,
49        _y: u32,
50        _antialias: &mut [AlphaU8],
51        _runs: &mut [AlphaRun],
52    ) {
53        unreachable!()
54    }
55
56    /// Blits a vertical run of pixels with a constant alpha value.
57    fn blit_v(&mut self, _x: u32, _y: u32, _height: LengthU32, _alpha: AlphaU8) {
58        unreachable!()
59    }
60
61    fn blit_anti_h2(&mut self, _x: u32, _y: u32, _alpha0: AlphaU8, _alpha1: AlphaU8) {
62        unreachable!()
63    }
64
65    fn blit_anti_v2(&mut self, _x: u32, _y: u32, _alpha0: AlphaU8, _alpha1: AlphaU8) {
66        unreachable!()
67    }
68
69    /// Blits a solid rectangle one or more pixels wide.
70    fn blit_rect(&mut self, _rect: &ScreenIntRect) {
71        unreachable!()
72    }
73
74    /// Blits a pattern of pixels defined by a rectangle-clipped mask.
75    fn blit_mask(&mut self, _mask: &Mask, _clip: &ScreenIntRect) {
76        unreachable!()
77    }
78}
tiny_skia/blitter.rs

tiny_skia/
blitter.rs
