Truble to get the color of a surface pixel

SDL Development
1

i need to get the color of a pixel of specific position of a surface,
i’m trying something like this:

int frogoutofbounds(SDL_Surface *maskbackground)
{
SDL_Color col;
Uint32 pixupleft;
SDL_PixelFormat fmt;
Uint8 r,g,b;
pixupleft=frog.pos.x+(frog.pos.y800);
fmt=maskbackground->format;
SDL_GetRGB(pixupleft,fmt,&r,&g,&b);
col.g=g;
printf(“green color:%d\n”,col.g);
…

but this don’t return me the rgb code, it returns me an non-sense
number that isn’t correct.

frog is a global struct that have the position of a sprite (frog.pos)
, i want to know if the upper left corner of the sprite (800x600
screen size) is over the “black zone” of the mask of the background.

thanks in advance–
f || www.ct.upc.edu/~ferran

2

You can check the pixel color with this function:

Uint32 GetPixel(SDL_Surface *surf, int x, int y)
{
//This function returns pixels color
int bpp = surf->format->BytesPerPixel;
Uint8 *p = (Uint8 *)surf->pixels + y * surf->pitch + x * bpp;

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

	case 2:
		return *(Uint16 *)p;

	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;
	
	case 4:
		return *(Uint32 *)p;
	
	default:
		return 0;
}

}

then use SDL_GetRGB to convert the Uint32 color value into pixel rgb format.—
http://gamescreators.sf.net Linux game developing community

----- Original Message -----
From: ferranf@gmail.com (f)
To: sdl at libsdl.org
Date: Mon, 3 Jul 2006 21:06:34 +0200
Subject: [SDL] truble to get the color of a surface pixel

i need to get the color of a pixel of specific position of a surface,
i’m trying something like this:

int frogoutofbounds(SDL_Surface *maskbackground)
{
SDL_Color col;
Uint32 pixupleft;
SDL_PixelFormat fmt;
Uint8 r,g,b;
pixupleft=frog.pos.x+(frog.pos.y800);
fmt=maskbackground->format;
SDL_GetRGB(pixupleft,fmt,&r,&g,&b);
col.g=g;
printf(“green color:%d\n”,col.g);
…

but this don’t return me the rgb code, it returns me an non-sense
number that isn’t correct.

frog is a global struct that have the position of a sprite (frog.pos)
, i want to know if the upper left corner of the sprite (800x600
screen size) is over the “black zone” of the mask of the background.

thanks in advance

–
f || www.ct.upc.edu/~ferran

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl

3

thanks!! :)On 7/4/06, antonmasteR wrote:

You can check the pixel color with this function:

Uint32 GetPixel(SDL_Surface *surf, int x, int y)
{
//This function returns pixels color
int bpp = surf->format->BytesPerPixel;
Uint8 *p = (Uint8 *)surf->pixels + y * surf->pitch + x * bpp;

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

            case 2:
                    return *(Uint16 *)p;

            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;

            case 4:
                    return *(Uint32 *)p;

            default:
                    return 0;
    }

}

then use SDL_GetRGB to convert the Uint32 color value into pixel rgb format.

http://gamescreators.sf.net Linux game developing community

-----Original Message-----
From: f <@f11>
To: sdl at libsdl.org
Date: Mon, 3 Jul 2006 21:06:34 +0200
Subject: [SDL] truble to get the color of a surface pixel

i need to get the color of a pixel of specific position of a surface,
i’m trying something like this:

int frogoutofbounds(SDL_Surface *maskbackground)
{
SDL_Color col;
Uint32 pixupleft;
SDL_PixelFormat fmt;
Uint8 r,g,b;
pixupleft=frog.pos.x+(frog.pos.y800);
fmt=maskbackground->format;
SDL_GetRGB(pixupleft,fmt,&r,&g,&b);
col.g=g;
printf(“green color:%d\n”,col.g);
…

but this don’t return me the rgb code, it returns me an non-sense
number that isn’t correct.

frog is a global struct that have the position of a sprite (frog.pos)
, i want to know if the upper left corner of the sprite (800x600
screen size) is over the “black zone” of the mask of the background.

thanks in advance

–
f || www.ct.upc.edu/~ferran

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl

–
f || www.ct.upc.edu/~ferran