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C-/C++-Quelltext

Uint8 rc, gc, bc, ac;

Quellcode

Invalid arguments ' Candidates are: void SDL_GetRGBA(unsigned int, const SDL_PixelFormat *, unsigned char *, unsigned char *, unsigned char *, unsigned char *) '

C-/C++-Quelltext

screen = SDL_SetVideoMode(800, 600, [b]16[/b], SDL_HWSURFACE);

C-/C++-Quelltext

screen = SDL_SetVideoMode(800, 600, [b]24[/b], SDL_HWSURFACE);

C-/C++-Quelltext

Uint32 ausgabe = SDL_MapRGBA(s->format, rc, gc, bc, ac);
cout << "Ausgabe: " << hex << ausgabe << endl;

C-/C++-Quelltext

SDL_GetRGBA(p, format, &rc, &gc, &bc, &ac);

C-/C++-Quelltext

screen = SDL_SetVideoMode(800, 600, 32, SDL_HWSURFACE);

C-/C++-Quelltext

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <SDL/SDL_image.h>
#include <SDL/SDL.h>
#include <SDL/SDL_gfxPrimitives.h>

using namespace std;

Uint32 getpixel(SDL_Surface *surface, int x, int y);
Uint32 getcolor(SDL_Surface *surface, int x, int y);

int main(void) {
    SDL_Surface *screen;
    SDL_Event event;
    Uint32 farbe = 0xff0000ff;

    int x, y;
    bool quit = false;

    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        cout << "Konnte SDL nicht initialisieren: %s\n" << SDL_GetError();
        return EXIT_FAILURE;
    }
    
    atexit(SDL_Quit);

    screen = SDL_SetVideoMode(800, 600, 32, SDL_HWSURFACE);
    if (screen == NULL) {
        cout << "Videomodus konnte nicht eingerichet werden: " << SDL_GetError()
                << endl;
        return EXIT_FAILURE;
    }

    x = (screen->w / 2);
    y = (screen->h / 2);

    boxRGBA(screen, 0, 0, 800, 600, 255, 255, 255, 255);
    SDL_WM_SetCaption("SDL_MapRGBA Test", 0);
    filledCircleColor(screen, x, y, 250, farbe);
    SDL_UpdateRect(screen, 0, 0, 0, 0);

    cout << "Referenzfarbe: " << hex << farbe << endl;
    cout << "Ausgelesene Farbe: " << hex << getcolor(screen, x, y) << endl;

    while (!quit) {
        if (SDL_WaitEvent(&event) && !quit) {
            switch (event.type) {
            case SDL_KEYDOWN:
                switch (event.key.keysym.sym) {
                case SDLK_ESCAPE:
                    quit = 1;
                    break;
                default:
                    break;
                }
                break;
            }
        }
    }
    return EXIT_SUCCESS;
}

Uint32 getcolor(SDL_Surface *surface, int x, int y) {
    Uint8 r, g, b, a;
    SDL_LockSurface(surface);
    SDL_PixelFormat *format = surface->format;
    Uint32 p = getpixel(surface, x, y);

    SDL_GetRGBA(p, format, &r, &g, &b, &a);
    SDL_UnlockSurface(surface);

    cout << endl;
    cout << "Ausgelesene einzelne 8-Bit Kanäle:" << endl;
    cout << "r: " << dec << (int) r << " g: " << (int) g << " b: " << (int) b
            << " alpha: " << (int) a << endl;
    cout << endl;

    Uint32 result = SDL_MapRGBA(surface->format, r, g, b, a);

    return result;
}

Uint32 getpixel(SDL_Surface *surface, int x, int y) {
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to retrieve */
    Uint8 *p = (Uint8 *) surface->pixels + y * surface->pitch + x * bpp;

    switch (bpp) {
    case 1:
        return *p;
        break;

    case 2:
        return *(Uint16 *) p;
        break;

    case 3:
        if (SDL_BYTEORDER == SDL_BIG_ENDIAN)
            return p[0] << 16 | p[1] << 8 | p[2];
        else
            return p[0] | p[1] << 8 | p[2] << 16;
        break;

    case 4:
        return *(Uint32 *) p;
        break;

    default:
        return 0; /* shouldn't happen, but avoids warnings */
    }
}

Quellcode

If the specified pixel format has no alpha component the alpha value will be ignored (as it will be in formats with a palette). 

C-/C++-Quelltext

boxRGBA(screen, 0, 0, 800, 600, 255, 255, 255, ALPHA);