多种颜色的C ++ DirectX DrawText

Question

I use ID3DXFont interface to draw text and that perfectly suits my needs as long as complete string is in single color. Now I'd wish to draw a string but in multiple colors. For instance "abc", with a in red, b in yellow, etc. I know that I could draw each letter on its own, giving a different Color parameter to DrawText each time. The only issue with this is that I do not know how many pixels should I offset after each letter because every letter has a different width. Hardcoding widths is not really a good solution.

Answer 1

The ID3DXFont interface doesn't allow you to draw multiple colors within a single invocation of DrawText . However, it can give you the bounding rectangles of any text that you wish to draw using the DT_CALCRECT flag, so you do not need to hardcode widths of particular glyphs within your font. This also means you can switch the font and/or size of the font without needing to modify your drawing code, or hardcoding new width. For example:

ID3DXFont* font = ...;
const char* strings[] = { "A", "i", "C" };
D3DCOLOR colors[] = { D3DCOLOR_ARGB(255, 255, 0, 0), D3DCOLOR_ARGB(255, 0, 255, 0), D3DCOLOR_ARGB(255, 0, 0, 255) };
RECT r = { 10,10,0,0}; // starting point
for (int i = 0; i < _countof(strings); ++i)
{
    font->DrawText(NULL, strings[i], -1, &r, DT_CALCRECT, 0);
    font->DrawText(NULL, strings[i], -1, &r, DT_NOCLIP, colors[i]);
    r.left = r.right; // offset for next character.
}

Note: I have used 'i' instead of 'b' from your example, because it makes it apparent that the rectangles are correct, as 'i' is (generally) a very thin glyph. Also note that this assumes a single line of text. The calculated rectangle also includes height, so if you are doing multiple lines, you could also use the height of the calculated rectangle to offset the position.