When the lines are not straight the antialiasing reduces the pixel
colors just a tad away from white. And then your use of nonzero
Amask in the SDL_CreateRGBSurface causes the SDL_gfx to go for
alpha blending. And without alpha channel set in your image you
get didley on the image.
I suggest you skip the alpha stuff unless you need it and use
SDL_DisplayFormat to get an image suitable for blitting.
You’re using ABGR, which on little endian machines happens to be what
the opengl wants (big endiand RGBA), but using that to blit
on screen in 2D is probably not what you’re looking for, because I’m
betting you’re display surface has something other than ABGR
(could it be ARGB?).
It’s been a while since I last played with SDL_gfx, so take all that
with some salt, but your example would seem to work ok if you set the
Amask to zero in the SDL_CreateRGBSurface call or use SDL_setAlpha(image,0,255);
to get something non-transparent on the surface.
However, I distinctly recall that there was fishy with SDL_gfx
and the way it handled the alpha channeling. Or to be more precice,
I never got it to work the way I was looking for, but it’s quite
likely I overlooked something as I was never really that
keen on getting it to work.
Maybe I’ll check back with an example …
cheers,
Tommi Kyntola
Armin Steinhoff wrote:> Hello,
I have a little bit trouble with the call ‘aalineRGBA’ from the SDL_Gfx library.
When I create a surface with a bpp of 32bit, ‘aalineRGBA’ draws only vertical and horizontal lines (ticks of a meter).
Only the start and end point of all other lines are drawn.
On a surface with 8 bpp all lines are drawn, but the color is wrong.
I have attached a short example. What’s wrong in my code? ( I’m working under SuSE LINUX 9.0. )
Thank you
Armin
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#include <stdlib.h>
#include <math.h>
#include “SDL.h”
#include “SDL_image.h”
#include “SDL_gfxPrimitives.h”
void cpoint(float rad, short cx, short cy, short radius, short * px, short * py)
{
// cx, cy are the center point of the circle
// px, py are points of the circle
*px = cx + (short)((float)radius * cosf(rad));
*py = cy + (short)((float)radius * sinf(rad));
}
int draw_tick(SDL_Surface * surf, float rad, short cx, short cy, short radius, short tick_len,
Uint8 r, Uint8 g, Uint8 b, Uint8 a )
{
short spx, spy, epx, epy;
cpoint(rad, cx, cy, radius, &spx, &spy);
cpoint(rad, cx, cy, radius - tick_len, &epx, &epy);
fprintf(stdout, "spx/spy %d,%d epx/epy: %d/%d\n", spx, spy, epx, epy);
return(aalineRGBA(surf, spx, spy, epx, epy, r, g, b, a));
}
int main()
{
SDL_Surface *display;
SDL_Surface *image;
int i, done, resp;
float rad;
SDL_Rect drect;
SDL_Rect srect;
SDL_Event event;
// init video stuff
if ( SDL_Init( SDL_INIT_VIDEO) < 0 )
{
fprintf(stderr, "SDL konnte nicht initialisiert werden: %s\n",
SDL_GetError());
exit(1);
}
atexit(SDL_Quit);
// init screen
display = SDL_SetVideoMode( 1024,768, 0, SDL_SWSURFACE);
if ( display == NULL )
{
fprintf(stderr, "SDL_SetVideoMode %s\n", SDL_GetError());
exit(1);
}
image = SDL_CreateRGBSurface(SDL_SWSURFACE, 1024, 768, 32, 0xFF, 0xFF00, 0xFF0000, 0xFF000000);
if ( image == NULL ) {
fprintf(stderr, "SDL_CreateRGBSurface: %s\n",SDL_GetError());
return(NULL);
}
//source rect
srect.x = 0;
srect.y = 0;
srect.w = (image->w);
srect.h = image->h;
// destination rect
drect.x = 0;
drect.y = 0;
drect.w = (image->w);
drect.h = image->h;
for (i=0; i < 360; i+=10)
{
rad = 6.28 * (float)i/360.0;
resp = draw_tick(image, rad, 150, 150, 50, 10, 255, 255, 255, 255 );
fprintf(stdout, "resp: %d\n", resp);
SDL_BlitSurface(image, &srect, display, &drect);
SDL_UpdateRects(display,1,&drect);
}
SDL_Delay(6000);
SDL_FreeSurface(image);
}
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