Is it possible to apply color gradients to rendered text?

Question

Ryan McCombe · Accepted Answer

Applying color gradients to rendered text 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 the text in a single color and then applying a gradient effect to the resulting surface. Here's a step-by-step method:

Render the text in a solid color (preferably white).
Create a surface with the desired gradient.
Use color modulation or alpha blending to combine the text and gradient.

Here's an example implementation of a horizontal gradient:

1#include <SDL.h>
2#include <SDL_ttf.h>
3
4SDL_Surface* createGradientSurface(
5  int width, int height, SDL_Color start,
6  SDL_Color end) {
7  SDL_Surface* surface = SDL_CreateRGBSurface(
8    0, width, height, 32, 0, 0, 0, 0);
9
10  for (int x = 0; x < width; ++x) {
11    float t = static_cast<float>(x) / (width -
12      1);
13    SDL_Color color = {
14      static_cast<Uint8>(start.r + t * (end.r -
15        start.r)),
16      static_cast<Uint8>(start.g + t * (end.g -
17        start.g)),
18      static_cast<Uint8>(start.b + t * (end.b -
19        start.b)),
20      255};
21    SDL_Rect rect = {x, 0, 1, height};
22    SDL_FillRect(surface, &rect,
23                 SDL_MapRGB(surface->format,
24                            color.r, color.g,
25                            color.b));
26  }
27
28  return surface;
29}
30
31SDL_Surface* applyGradientToText(
32  TTF_Font* font, const char* text,
33  SDL_Color start, SDL_Color end) {
34  // Render text in white
35  SDL_Surface* textSurface =
36    TTF_RenderText_Blended(font, text,
37                           {
38                             255, 255, 255,
39                             255});
40  if (!textSurface) return nullptr;
41
42  // Create gradient surface
43  SDL_Surface* gradientSurface =
44    createGradientSurface(textSurface->w,
45                          textSurface->h, start,
46                          end);
47  if (!gradientSurface) {
48    SDL_FreeSurface(textSurface);
49    return nullptr;
50  }
51
52  // Apply gradient to text
53  SDL_BlitSurface(textSurface, nullptr,
54                  gradientSurface, nullptr);
55  SDL_SetSurfaceBlendMode(textSurface,
56                          SDL_BLENDMODE_MOD);
57  SDL_BlitSurface(gradientSurface, nullptr,
58                  textSurface, nullptr);
59
60  SDL_FreeSurface(gradientSurface);
61  return textSurface;
62}
63
64// Usage
65TTF_Font* font = TTF_OpenFont("font.ttf", 24);
66SDL_Color startColor = {255, 0, 0, 255}; // Red
67SDL_Color endColor = {0, 0, 255, 255}; // Blue
68
69SDL_Surface* gradientTextSurface =
70  applyGradientToText(font, "Gradient Text",
71                      startColor, endColor);
72
73// Render gradientTextSurface to your screen
74SDL_BlitSurface(gradientTextSurface, nullptr,
75                screenSurface, &dstRect);
76
77// Clean up
78SDL_FreeSurface (gradientTextSurface);
79TTF_CloseFont (font);

This example creates a horizontal gradient, but you can modify the createGradientSurface function to create different types of gradients (vertical, radial, etc.). For more complex gradients or better performance, consider using SDL2's hardware acceleration features or a dedicated graphics library.

Remember that this technique may not work perfectly for all fonts, especially those with anti-aliasing. You might need to adjust the blending mode or use a different approach for the best results with your specific fonts and gradients.

Rendering Text with `SDL_ttf`

Applying Color Gradients to Text

Rendering Text with `SDL_ttf`

Game Development with SDL2

Questions & Answers

Applying Color Gradients to Text

Rendering Text with SDL_ttf

Questions & Answers

Rendering Text with `SDL_ttf`