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font/freetype: Rewrite monoToGrayscale algorithm

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The original version had issues converting properly and caused broken
glyphs. This version tries to be as simple as possible in order to make
it easy to understand. I haven't measured the performance but in
practice this will only happen during the first render of the glyph
after a face change (i.e. during launch or when changing font size).
This commit is contained in:
sin-ack
2024-12-29 02:05:37 +00:00
parent 5293fc9c2f
commit bfde326bcb
1 changed files with 7 additions and 19 deletions
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26
src/font/face/freetype_convert.zig
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@ -43,28 +43,16 @@ pub fn monoToGrayscale(alloc: Allocator, bm: Bitmap) Allocator.Error!Bitmap {
var buf = try alloc.alloc(u8, bm.width * bm.rows);
errdefer alloc.free(buf);
// width divided by 8 because each byte has 8 pixels. This is therefore
// the number of bytes in each row.
const bytes_per_row = bm.width >> 3;
var source_i: usize = 0;
var target_i: usize = 0;
var i: usize = bm.rows;
while (i > 0) : (i -= 1) {
var j: usize = bytes_per_row;
while (j > 0) : (j -= 1) {
var bit: u4 = 8;
while (bit > 0) : (bit -= 1) {
const mask = @as(u8, 1) << @as(u3, @intCast(bit - 1));
const bitval: u8 = if (bm.buffer[source_i + (j - 1)] & mask > 0) 0xFF else 0;
buf[target_i] = bitval;
target_i += 1;
for (0..bm.rows) |y| {
const row_offset = y * @as(usize, @intCast(bm.pitch));
for (0..bm.width) |x| {
const byte_offset = row_offset + @divTrunc(x, 8);
const mask = @as(u8, 1) << @intCast(7 - (x % 8));
const bit: u8 = @intFromBool((bm.buffer[byte_offset] & mask) != 0);
buf[y * bm.width + x] = bit * 255;
}
}
source_i += @intCast(bm.pitch);
}
var copy = bm;
copy.buffer = buf.ptr;
copy.pixel_mode = freetype.c.FT_PIXEL_MODE_GRAY;