Adjusting Text Kerning and Letter Spacing
How can I implement text kerning or letter-spacing adjustments with SDL_ttf?
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.
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