Text Performance, Fitting and Wrapping

Adjusting Text Kerning and Letter Spacing

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

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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:

#include <SDL.h>
#include <SDL_ttf.h>

#include <string>
#include <vector>

class KernedText : public Text {
public:
  KernedText(std::string Content, int FontSize,
             int LetterSpacing)
    : Text{FontSize},
      LetterSpacing{LetterSpacing} {
    CreateSurface(Content);
  }

private:
  void CreateSurface(
    const std::string& Content) {
    std::vector<SDL_Surface*> CharSurfaces;
    int TotalWidth{0};
    int MaxHeight{0};

    // Render each character separately
    for (char c : Content) {
      SDL_Surface* CharSurface =
        TTF_RenderGlyph_Blended(
          Font, c, {255, 255, 255, 255});
      if (CharSurface) {
        CharSurfaces.push_back(CharSurface);
        TotalWidth += CharSurface->w +
          LetterSpacing;
        MaxHeight = std::max(
          MaxHeight, CharSurface->h);
      }
    }

    // Create a surface to hold all characters
    TextSurface =
      SDL_CreateRGBSurface(0, TotalWidth,
                           MaxHeight, 32, 0, 0,
                           0, 0);

    // Blit each character onto the main surface
    int XPos{0};
    for (auto* CharSurface : CharSurfaces) {
      SDL_Rect DestRect{
        XPos, 0, CharSurface->w,
        CharSurface->h};
      SDL_BlitSurface(CharSurface, nullptr,
                      TextSurface, &DestRect);
      XPos += CharSurface->w + LetterSpacing;
      SDL_FreeSurface(CharSurface);
    }
  }

  int LetterSpacing;
};

int main() {
  SDL_Init(SDL_INIT_VIDEO);
  TTF_Init();

  KernedText MyText{"Hello World", 24, 5};

  // Rest of your SDL setup and rendering loop...

  TTF_Quit();
  SDL_Quit();
  return 0;
}

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.

Answers to questions are automatically generated and may not have been reviewed.

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