Is it possible to render text along a curved path?

Question

Ryan McCombe · Accepted Answer

Rendering text along a curved path is possible with SDL2 and SDL_ttf, but it requires a custom implementation as there's no built-in function for this. The basic approach involves rendering individual characters and positioning them along the curve. Here's a step-by-step method:

Define the curve mathematically (e.g., using a Bzier curve or a simple arc).
Render each character separately.
Calculate the position and rotation for each character along the curve.
Blit each character onto the destination surface with the calculated transformation.

Here's a simple example that renders text along a circular arc:

1#include <SDL.h>
2#include <SDL_ttf.h>
3
4#include <cmath>
5#include <string>
6
7void renderTextAlongCurve(SDL_Surface* dest,
8                          TTF_Font* font,
9                          const std::string&
10                          text, int centerX,
11                          int centerY,
12                          int radius,
13                          double startAngle,
14                          SDL_Color color) {
15  double angle = startAngle;
16  double angleStep = 0.1;
17  // Adjust for tighter/looser curve
18
19  for (char c : text) {
20    SDL_Surface* charSurface =
21      TTF_RenderGlyph_Blended(font, c, color);
22    if (!charSurface) continue;
23
24    double x = centerX + radius * cos(angle);
25    double y = centerY + radius * sin(angle);
26
27    SDL_Rect dstRect = {
28      static_cast<int>(x - charSurface->w / 2),
29      static_cast<int>(y - charSurface->h / 2),
30      0, 0};
31
32    // Simple rotation (for more accurate rotation, use SDL_gfx)
33    SDL_BlitSurface(charSurface, nullptr, dest,
34                    &dstRect);
35
36    SDL_FreeSurface(charSurface);
37
38    angle += angleStep;
39  }
40}
41
42// Usage
43renderTextAlongCurve(
44  screenSurface, font,
45  "Curved Text Example",
46  300, 300, 100,  M_PI,
47  {255, 255, 255, 255}
48);

This example renders text along a circular path. For more complex curves:

Replace the circular math with your curve function.
Implement proper character rotation (SDL2_gfx library can help).
Adjust character spacing based on the curve's curvature.

Note that this method may not produce perfect results for all fonts or curves. For production use, consider using a more sophisticated graphics library or implementing a more advanced text layout system.

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