Rotating sprite with a center of rotation in SDL2 - c

Question

I want to rotate a sprite in C and SDL2, with a set center of rotation, and without scaling or anti-aliasing.
My game resolution is 320x240, and the display is scaled up when I set the game to full screen, because I'm using SDL_RenderSetLogicalSize(renderer, 320, 240).
Using SDL2's SDL_RenderCopyEx() (or SDL_RenderCopyExF()) to rotate a SDL_Texture.
As shown in this example ( https://imgur.com/UGNDfEY ) when the window is set to full screen, the texture is scaled up and at much higher resolution. Is would like the final 320x240 rendering to be scaled up, not the individual textures.
Using SDL_gfx's rotozoomSurface() was a possible alternative.
However, as shown in this example ( https://imgur.com/czPEUhv ), while this method give the intended low-resolution and aliased look, it has no center of rotation, and renders the transparency color as half-transparent black.
Is there a function that does what I'm looking for? Are there some tricks to get around that?

Answer 1

What I would do is to render what you want to in a SDL_Texture, and then print this texture into the renderer, using something like :
// Set 'your_texture' as target
SDL_SetRenderTarget(your_renderer, your_texture);
// We are now printing the rotated image on the texture
SDL_RenderCopyEx(your_renderer, // we still use the renderer; it will be automatically printed into the texture 'your_texture'
your_image,
&srcrect,
&dstrect,
angle,
&center,
SDL_FLIP_NONE); // unless you want to flip vertically / horizontally
// Set the renderer as target and print the previous texture
SDL_SetRenderTarget(your_renderer, NULL);
SDL_RenderClear(your_renderer);
SDL_RenderCopy (your_renderer, your_texture, NULL, NULL); // here the scale is automatically done
SDL_RenderPresent(your_renderer);
It works, but I don't know if it is very efficient.
Don't forget to define your_texture with a SDL_TEXTUREACCESS_TARGET access.
Hope this helps,
Durza42

Answer 2

Thanks to #Durza42, here's the solution to my problem:
#define kScreenWidth 320
#define kScreenHeight 240
SDL_Window* g_window = NULL;
SDL_Texture* g_texture = NULL;
SDL_Renderer* g_renderer = NULL;
SDL_Texture* g_sprite = NULL;
double g_sprite_angle = 0.0;
SDL_FRect g_sprite_frect = {
.x = 50.0f,
.y = 50.0f,
.w = 32.0f,
.h = 32.0f,
};
void
sdl_load(void)
{
SDL_Init(SDL_INIT_VIDEO);
g_window = SDL_CreateWindow(NULL, SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, kScreenWidth, kScreenHeight, 0);
g_renderer = SDL_CreateRenderer(g_window, -1, SDL_RENDERER_PRESENTVSYNC);
g_texture = SDL_CreateTexture(g_renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, kScreenWidth, kScreenHeight);
SDL_RenderSetLogicalSize(g_renderer, kScreenWidth, kScreenHeight);
}
void
sprite_load(void)
{
g_sprite = IMG_LoadTexture(g_renderer, "./sprite.png");
}
void
draw(void)
{
SDL_SetRenderTarget(g_renderer, g_texture);
SDL_RenderClear(g_renderer);
SDL_RenderCopyExF(g_renderer, g_sprite, NULL, &g_sprite_frect, g_sprite_angle, NULL, SDL_FLIP_NONE);
SDL_SetRenderTarget(g_renderer, NULL);
SDL_RenderClear(g_renderer);
SDL_RenderCopy(g_renderer, g_texture, NULL, NULL);
SDL_RenderPresent(g_renderer);
}