stb_truetype calculating the dimensions of a string

Question

I'm using stb_truetype to render TrueType fonts in an OpenGL context.

Is there any simple way to pre-determine the height and width of a string in the font before it is rendered?

Answer 1

LWJGL STB True Type demo contains an implementation for this now (since August 2017), including kerning:

lwjgl3 / Truetype.java:

private float getStringWidth(STBTTFontinfo info, String text, int from, int to, int fontHeight) {
    int width = 0;

    try (MemoryStack stack = stackPush()) {
        IntBuffer pCodePoint       = stack.mallocInt(1);
        IntBuffer pAdvancedWidth   = stack.mallocInt(1);
        IntBuffer pLeftSideBearing = stack.mallocInt(1);

        int i = from;
        while (i < to) {
            i += getCP(text, to, i, pCodePoint);
            int cp = pCodePoint.get(0);

            stbtt_GetCodepointHMetrics(info, cp, pAdvancedWidth, pLeftSideBearing);
            width += pAdvancedWidth.get(0);

            if (isKerningEnabled() && i < to) {
                getCP(text, to, i, pCodePoint);
                width += stbtt_GetCodepointKernAdvance(info, cp, pCodePoint.get(0));
            }
        }
    }

    return width * stbtt_ScaleForPixelHeight(info, fontHeight);
}

private static int getCP(String text, int to, int i, IntBuffer cpOut) {
    char c1 = text.charAt(i);
    if (Character.isHighSurrogate(c1) && i + 1 < to) {
        char c2 = text.charAt(i + 1);
        if (Character.isLowSurrogate(c2)) {
            cpOut.put(0, Character.toCodePoint(c1, c2));
            return 2;
        }
    }
    cpOut.put(0, c1);
    return 1;
}