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zig/comptimeFont.zig

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+// https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6cmap.html
+const std = @import("std");
+const readInt = std.mem.readInt;
+const assert = std.debug.assert;
+const font = @import("main.zig").defaultFont;
+
+fn sort(array: []const u16) []const u16 {
+    var tempArray: [1]u16 = undefined;
+    @setEvalBranchQuota(10000);
+    if(array.len == 1) {
+        tempArray[0] = array[0];
+        return &tempArray;
+    } else {
+        const indexofMin = std.mem.indexOfMin(u16, array);
+        tempArray[0] = array[indexofMin];
+        return &tempArray ++ sort(array[0..indexofMin] ++ array[indexofMin + 1..]);
+    }
+}
+
+const bytes = font.ttf_bytes;
+const tableStart = font.index_map;
+const format = std.mem.readInt(u16, bytes[tableStart..][0..2], .big);
+
+// Apple: "The segCount is the number of contiguous code ranges in the font"
+const seg_count = readInt(u16, bytes[tableStart + 6 ..][0..2], .big) >> 1;
+
+const firstEndCode = tableStart + 14;
+const lastEndCode = firstEndCode + (2 * seg_count);
+const endCodes = eds: {
+    var codes: [seg_count]u16 = undefined;
+    // apple: "The segments are sorted in order of increasing endCode values."
+    for(0..seg_count) |i| {
+        codes[i] = readInt(u16, bytes[firstEndCode .. lastEndCode][(2 * i)..(2 * i) + 2], .big);
+    }
+    assert(codes[seg_count - 1] == 0xFFFF);
+    break :eds codes;
+};
+
+test "endCodes are sorted" {
+    var last = endCodes[0];
+    for(endCodes[1..]) |code| {
+        std.debug.assert(code > last);
+        last = code;
+    }
+}
+
+// 2 bytes reserved, then start codes
+const reservedPad = readInt(u16, bytes[lastEndCode..lastEndCode + 2], .big);
+const _ = blk: {
+    assert(reservedPad == 0);
+    break :blk;
+};
+
+const firstStartCode = lastEndCode + 4;
+const startCodes = sts: {
+    var codes: [seg_count]u16 = undefined;
+    codes[0] = 0;
+    for(1..seg_count) |i| {
+        codes[i] = readInt(u16,  bytes[firstStartCode .. firstStartCode + (2 * seg_count)][(2 * i)..(2 * i) + 2], .big);
+    }
+    const codesSorted = sort(&codes);
+    break :sts codesSorted;
+};
+
+test "startCodes are sorted" {
+    var last = startCodes[0];
+    for(startCodes[1..]) |code| {
+        std.debug.assert(code >= last);
+        last = code;
+    }
+}
+
+test "codepoint array lengths match" {
+    std.debug.assert(format == 4);
+    std.debug.assert(endCodes.len == startCodes.len);
+    @compileLog("endCodes len", endCodes.len);
+    @compileLog("startCodes len", startCodes.len);
+
+    const altEndCodes = std.mem.bytesAsSlice(u16, bytes[firstEndCode .. lastEndCode]);
+    std.debug.assert(!std.mem.eql(u16, &endCodes, @alignCast(@constCast(altEndCodes))));
+    @compileLog("altEndCodes (bytesAsSlice method) len", altEndCodes.len);
+}
+
+pub const codePoints = cps: {
+    const totalCodeCount = cnt: {
+        var count = 0;
+        for(startCodes, endCodes) |start, end| {
+            count += (end - start);
+        }
+        break :cnt count;
+    };
+
+    const allCodes = cds: {
+        var codes: [totalCodeCount]i32 = undefined;
+        var codesIdx = 0;
+        @setEvalBranchQuota(10000);
+        for(startCodes,endCodes) |start, end| {
+            for(start..end) |n| {
+                codes[codesIdx] = n;
+                codesIdx += 1;
+            }
+        }
+        break :cds codes;
+    };
+    break :cps allCodes;
+};