Text Performance, Fitting and Wrapping

Adjusting Text Kerning and Letter Spacing

How can I implement text kerning or letter-spacing adjustments with SDL_ttf?

3D art representing computer programming

Implementing text kerning or letter-spacing adjustments with SDL_ttf requires a bit of manual work, as SDL_ttf doesn't provide direct functions for these features. However, we can achieve these effects by rendering individual characters and positioning them manually.

Here's an approach to implement custom letter spacing:

1#include <SDL.h>
2#include <SDL_ttf.h>
3
4#include <string>
5#include <vector>
6
7class KernedText : public Text {
8public:
9  KernedText(std::string Content, int FontSize,
10             int LetterSpacing)
11    : Text{FontSize},
12      LetterSpacing{LetterSpacing} {
13    CreateSurface(Content);
14  }
15
16private:
17  void CreateSurface(
18    const std::string& Content) {
19    std::vector<SDL_Surface*> CharSurfaces;
20    int TotalWidth{0};
21    int MaxHeight{0};
22
23    // Render each character separately
24    for (char c : Content) {
25      SDL_Surface* CharSurface =
26        TTF_RenderGlyph_Blended(
27          Font, c, {255, 255, 255, 255});
28      if (CharSurface) {
29        CharSurfaces.push_back(CharSurface);
30        TotalWidth += CharSurface->w +
31          LetterSpacing;
32        MaxHeight = std::max(
33          MaxHeight, CharSurface->h);
34      }
35    }
36
37    // Create a surface to hold all characters
38    TextSurface =
39      SDL_CreateRGBSurface(0, TotalWidth,
40                           MaxHeight, 32, 0, 0,
41                           0, 0);
42
43    // Blit each character onto the main surface
44    int XPos{0};
45    for (auto* CharSurface : CharSurfaces) {
46      SDL_Rect DestRect{
47        XPos, 0, CharSurface->w,
48        CharSurface->h};
49      SDL_BlitSurface(CharSurface, nullptr,
50                      TextSurface, &DestRect);
51      XPos += CharSurface->w + LetterSpacing;
52      SDL_FreeSurface(CharSurface);
53    }
54  }
55
56  int LetterSpacing;
57};
58
59int main() {
60  SDL_Init(SDL_INIT_VIDEO);
61  TTF_Init();
62
63  KernedText MyText{"Hello World", 24, 5};
64
65  // Rest of your SDL setup and rendering loop...
66
67  TTF_Quit();
68  SDL_Quit();
69  return 0;
70}

In this example, we create a KernedText class that extends our Text class. It renders each character separately and then combines them into a single surface, allowing us to control the spacing between letters.

To implement kerning, you'd need to use TTF_GetFontKerningSizeGlyphs() to get the kerning value between pairs of characters and adjust the positioning accordingly.

Remember that manually rendering characters like this can be less efficient than using SDL_ttf's built-in text rendering functions, so use this approach judiciously, especially for large amounts of text or when performance is critical.

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