SDL2 How can I render pixels from raw format? - c

Question

I am trying to render a custom image and it requires that I load the file into memory and render it out through SDL. The image is a raw format and I think if I could render
My code might be garbage , so I am open to changes with it.
void Create_SDL_Window()
{
SDL_Init(SDL_INIT_EVERYTHING);
IMG_Init(IMG_INIT_PNG);
window = SDL_CreateWindow("Test Window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
renderer = SDL_CreateRenderer(window, -1, 0);
printf("Window And Renderer Created!\n");
}
int main(){
FILE* customImage = fopen(Path, "rb");
Create_SDL_Window();
while (!quit){
void *p;
p = customImage;
SDL_Texture* buffer = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_BGRA8888,SDL_TEXTUREACCESS_STREAMING, 800, 600);
SDL_LockTexture(buffer, NULL, &p, &pitch);
SDL_UnlockTexture(buffer);
SDL_RenderCopy(renderer, buffer, NULL, NULL);
SDL_RenderPresent(renderer);
while (SDL_PollEvent(&e)){
//If user closes the window
if (e.type == SDL_QUIT){
quit = true;
}
//If user presses any key
if (e.type == SDL_KEYDOWN){
// quit = true;
}
//If user clicks the mouse
if (e.type == SDL_MOUSEBUTTONDOWN){
/// quit = true;
}
}
SDL_RenderPresent(renderer);
}

Answer 1

You have things backwards. You should notice that SDL_LockTexture takes a pointer-to-a-pointer. This is because SDL already has a buffer appropriately sized for the texture and it needs to tell you the address (and pitch) so that you can write to this buffer.
You also have the problem that you think you can use a FILE* as a pixel buffer. This is not true at all; FILE* is a pointer to a structure describing the file, not its contents.
What you need to do is something like:
// create your empty texture
...
int pitch = 0;
char* p = NULL;
SDL_LockTexture(buffer, NULL, &p, &pitch);
... // Error checking
// now open your file and mmap it
int fd = open(Path, O_RDONLY);
struct stat sb;
fstat(fd, &sb);
const char* memblock = mmap(NULL, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
... // Error checking
// now you need to copy the data from the file to the pixel buffer
// you claim you are working with 800x600 32bit image data
for (int y = 0; y < 600; ++y)
{
const char* src = &memblock[y * pitch]; // is this really the pitch of the file? you didn't specify....
char* dst = &p[y * pitch];
memcpy(dst, src, 800*4); // width * size of a pixel
}
this code assumes you didn't make a mistake somewhere else such as the size of the texture or the format of the pixels. You will also notice some unknowns in the code you need to find out.
You might also try SDL_UpdateTexture which will accept a pointer to pixels like you are attempting in your code. However, it is likely to be much slower than SDL_LockTexture and you still need to actually read the file (or better yet mmap it) to get the pixels to pass in.
Yet a 3rd option, if SDL_Image knows how to read your "RAW" file, is to use IMG_Load to get an SDL_Surface of your image then creating a texture from that surface using SDL_CreateTextureFromSurface