im fairly new to assembly and im having trouble accessing some data from an SDL_Surface struct (it''s definition is below my function).
i''ve tried doing a couple of different things like
MOV EDX, surface
IMUL someReg, [EDX+16] // surface->pitch ???
this is the code im writing :
static void putpixel24(SDL_Surface *surface, int x, int y, uint32 color)
{
//
// How do i access surface->pitch in assembly?
//
uint32 pitch = surface->pitch;
// EDX = SDL_Surface *surface
__asm mov edx, surface
// move address of surface->pixels into EBX
__asm mov ebx, [edx+20]
// EAX = y * surface->pitch
__asm mov eax, y
__asm imul eax, pitch //<---------- ?
__asm add ebx, eax
// x * 3 (using adds instead of imuls)
__asm add ebx, x
__asm add ebx, x
__asm add ebx, x
// [ebx] is now the address of the pixel we wish to change
__asm mov eax, color
__asm mov [ebx], al
__asm shr eax, 8
__asm mov [ebx+1], ax
}
this is the definition of an SDL_Surface:
typedef struct SDL_Surface {
Uint32 flags; /* Read-only */
SDL_PixelFormat *format; /* Read-only */
int w, h; /* Read-only */
Uint16 pitch; /* Read-only */
void *pixels; /* Read-write */
int offset; /* Private */
/* Hardware-specific surface info */
struct private_hwdata *hwdata;
/* clipping information */
SDL_Rect clip_rect; /* Read-only */
Uint32 unused1; /* for binary compatibility */
/* Allow recursive locks */
Uint32 locked; /* Private */
/* info for fast blit mapping to other surfaces */
struct SDL_BlitMap *map; /* Private */
/* format version, bumped at every change to invalidate blit maps */
unsigned int format_version; /* Private */
/* Reference count -- used when freeing surface */
int refcount; /* Read-mostly */
} SDL_Surface;
PS...i know this function would probably be faster written in C++, im just trying to learn new things.
