feat(media): implement native JPEG coding and bounded MJPEG streaming

packages/image/src/jpeg_dct.zigadded+39-0

Changes to packages/image/src/jpeg_dct.zig

		@@ -0,0 +1,39 @@
	1	+//! Shared orthonormal JPEG DCT basis and inverse transform (Home, MIT).
	2	+const std = ;
	3	+pub const BASIS: [8]@Vector(8, f32) = blk: {
	4	+ @setEvalBranchQuota(10000);
	5	+ var b: [8]@Vector(8, f32) = undefined;
	6	+ for (0..8) |u| for (0..8) |x| {
	7	+ const scale: f64 = if (u == 0) 0.3535533905932738 else 0.5;
	8	+ b[u][x] = @floatCast(scale * @cos((@as(f64, @floatFromInt(x)) * 2 + 1) * @as(f64, @floatFromInt(u)) * std.math.pi / 16));
	9	+ };
	10	+ break :blk b;
	11	+};
	12	+
	13	+pub fn inverse(block: *[64]i32, quant: *const [64]u16) void {
	14	+ var work: [8][8]f32 = undefined;
	15	+ for (0..8) |v| {
	16	+ var coefficients: @Vector(8, f32) = undefined;
	17	+ inline for (0..8) |u| coefficients[u] = @as(f32, @floatFromInt(block[v * 8 + u])) * @as(f32, @floatFromInt(quant[v * 8 + u]));
	18	+ for (0..8) |x| {
	19	+ var basis: @Vector(8, f32) = undefined;
	20	+ inline for (0..8) |u| basis[u] = BASIS[u][x];
	21	+ work[v][x] = @reduce(.Add, coefficients * basis);
	22	+ }
	23	+ }
	24	+ for (0..8) |y| for (0..8) |x| {
	25	+ var values: @Vector(8, f32) = undefined;
	26	+ var basis: @Vector(8, f32) = undefined;
	27	+ inline for (0..8) |v| {
	28	+ values[v] = work[v][x];
	29	+ basis[v] = BASIS[v][y];
	30	+ }
	31	+ block[y * 8 + x] = @intFromFloat(std.math.clamp(@round(@reduce(.Add, values * basis)) + 128, 0, 255));
	32	+ };
	33	+}
	34	+test "inverse JPEG DC scale and zero AC are exact" {
	35	+ var block: [64]i32 = @splat(0);
	36	+ block[0] = 80;
	37	+ inverse(&block, &@as([64]u16, @splat(1)));
	38	+ for (block) |v| try std.testing.expectEqual(@as(i32, 138), v);
	39	+}