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avoid an alloc and buffer copy in the common case on font loading

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This commit is contained in:
Mitchell Hashimoto
2022-08-19 15:12:57 -07:00
parent 742dd010eb
commit f9313801f1
2 changed files with 32 additions and 18 deletions
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5
src/Atlas.zig
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@ -93,6 +93,11 @@ pub fn reserve(self: *Atlas, alloc: Allocator, width: u32, height: u32) !Region
// x, y are populated within :best_idx below
var region: Region = .{ .x = 0, .y = 0, .width = width, .height = height };
// If our width/height are 0, then we return the region as-is. This
// may seem like an error case but it simplifies downstream callers who
// might be trying to write empty data.
if (width == 0 and height == 0) return region;
// Find the location in our nodes list to insert the new node for this region.
var best_idx: usize = best_idx: {
var best_height: u32 = std.math.maxInt(u32);

45
src/font/Face.zig
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@ -88,6 +88,7 @@ pub fn loadGlyph(self: Face, alloc: Allocator, atlas: *Atlas, cp: u32) !Glyph {
const glyph = self.ft_face.*.glyph;
const bitmap = glyph.*.bitmap;
assert(bitmap.pixel_mode == ftc.FT_PIXEL_MODE_GRAY);
const src_w = bitmap.width;
const src_h = bitmap.rows;
@ -96,25 +97,33 @@ pub fn loadGlyph(self: Face, alloc: Allocator, atlas: *Atlas, cp: u32) !Glyph {
const region = try atlas.reserve(alloc, tgt_w, tgt_h);
// Build our buffer
//
// TODO(perf): we can avoid a buffer copy here in some cases where
// tgt_w == bitmap.width and bitmap.width == bitmap.pitch
const buffer = try alloc.alloc(u8, tgt_w * tgt_h);
defer alloc.free(buffer);
var dst_ptr = buffer;
var src_ptr = bitmap.buffer;
var i: usize = 0;
while (i < src_h) : (i += 1) {
std.mem.copy(u8, dst_ptr, src_ptr[0..bitmap.width]);
dst_ptr = dst_ptr[tgt_w..];
src_ptr += @intCast(usize, bitmap.pitch);
}
// If we have data, copy it into the atlas
if (region.width > 0 and region.height > 0) {
// We can avoid a buffer copy if our atlas width and bitmap
// width match and the bitmap pitch is just the width (meaning
// the data is tightly packed).
const needs_copy = !(tgt_w == bitmap.width and bitmap.width == bitmap.pitch);
// Write the glyph information into the atlas
assert(region.width == tgt_w);
assert(region.height == tgt_h);
atlas.set(region, buffer);
// If we need to copy the data, we copy it into a temporary buffer.
const buffer = if (needs_copy) buffer: {
var temp = try alloc.alloc(u8, tgt_w * tgt_h);
var dst_ptr = temp;
var src_ptr = bitmap.buffer;
var i: usize = 0;
while (i < src_h) : (i += 1) {
std.mem.copy(u8, dst_ptr, src_ptr[0..bitmap.width]);
dst_ptr = dst_ptr[tgt_w..];
src_ptr += @intCast(usize, bitmap.pitch);
}
break :buffer temp;
} else bitmap.buffer[0..(tgt_w * tgt_h)];
defer if (buffer.ptr != bitmap.buffer) alloc.free(buffer);
// Write the glyph information into the atlas
assert(region.width == tgt_w);
assert(region.height == tgt_h);
atlas.set(region, buffer);
}
// Store glyph metadata
return Glyph{