Creating texture and palette modification

Question

I need to create a texture from a surface with indexed color palette and alter the colors. However, after I set new colors, the rendered texture gets blank.

int main(int argc, char** argv)
{
    init();

    gSurface = TTF_RenderText_Solid(gFont, "text", fg1);

    // text is rendered properly, without following line
    SDL_SetPaletteColors(gSurface->format->palette, &fg2, 1, 1);

    gTexture = SDL_CreateTextureFromSurface(gRenderer, gSurface);

    SDL_SetRenderDrawColor(gRenderer, 255, 255, 255, 255);
    SDL_RenderClear(gRenderer);

    SDL_RenderCopy(gRenderer, gTexture, NULL, NULL);
    SDL_RenderPresent(gRenderer);

    SDL_Delay(1000);

    quit();
}

I tested this code with software rendering using window surface instead of renderer and pallete changing worked.
Could someone explain me why does it happed and how to fix it?

Answer 1

I think your problem is the fact that SDL_SetPaletteColors wants an array of SDL_Colors as an argument instead of pointer to a single color. I cannot guarantee that this is the problem as you didn't post the code where you initialize the code, and you haven't told if SDL_GetError() returns an error message.

Otherwise, make sure to always check what SDL_GetError() returns on a SDL function you think might be the cause of the problem.

Answer 2

Some days ago I have encountered a similar issue with a short example SDL2 app. There were no mainloop as in your sample code. After mainloop added the image began to display.

Quick fix for your code seems to be: Put SDL_Delay(10); or SDL_Delay(100); between SDL_RenderCopy and SDL_RenderPresent. Just like that

SDL_SetRenderDrawColor(gRenderer, 255, 255, 255, 255);
SDL_RenderClear(gRenderer);

SDL_RenderCopy(gRenderer, gTexture, NULL, NULL);
SDL_Delay(10);
SDL_RenderPresent(gRenderer);

SDL_Delay(1000);