SDL Clipping

[John Spikowski]

I was wondering if any of the graphics pros here might offer some guidance with a strange issue I having with SDL. I'm trying to combine the functionally of both the BBC and SDL_draw extension libraries and I have this strange issue. I was hoping I could take advantage of the BBC clipping features of the library that SDL_draw doesn't offer. Clipping works great on the vertical axis but wraps the clipped image horizontal. Searching the net I have seen OpenGL settings to control edge clipping and so on. Is there a SDL option on window creation to prevent the wrapping effect and clip like the vertical axis?

[Charles Pegge]

I don't know much about SDL but, the docs say you can set a clipping rectangle (prior to drawing something)

http://search.cpan.org/~wkeenan/SDL-...ce.pm#Clipping

[John Spikowski]

Thanks Charles for the tip but my last attempt didn't work either. (see attached image) I used the SDL_SetClipRect hoping that would work but no luck.

  screen = SDL_SetVideoMode(width, height, 32, videoflags);
  SDL_SetClipRect(screen, NULL);

[John Spikowski]

Well, it looks like this isn't a BBC issue as it does the same thing when using SDL_draw alone. The SDL_SetClipRect did seem to prevent the seg fault I was getting when rendering off screen without the call. If I can get by the horizontal wrapping SDL is imposing, I won't need BBC for the clipping support. Any ideas are welcome and appreciated.

With a bit more testing it looks like it does seg fault if I render vertically off screen using SDL_draw alone. If I can solve this wrapping issue I can make SDL_draw clipping work in conjunction with the BBC extension module.

I noticed that passing a NULL for the RECT structure disabled clipping which is the opposite effect of what I was looking for. I changed my SDL_draw window create function to pass a valid RECT structure. Here is my code that still doesn't work and wraps the image.

SB Draw extension module source

besFUNCTION(SDL_Draw_Window)
  DIM AS int width, height;
  DIM AS Uint32 videoflags;
  DIM AS const char PTR title;
  DIM AS SDL_Rect screct;
  SDL_Init(SDL_INIT_VIDEO);
  atexit(SDL_Quit);
  videoflags = SDL_SWSURFACE | SDL_ANYFORMAT;
  besARGUMENTS("ii[z]")
    AT width, AT height, AT title
  besARGEND
  IF (title EQ NULL) THEN_DO title = "";
  screen = SDL_SetVideoMode(width, height, 32, videoflags);
  screct.x = 0;
  screct.y = 0;
  screct.w = 800;  
  screct.h = 600;  
  SDL_SetClipRect(screen, AT screct);
  SDL_WM_SetCaption(title, 0);
  besRETURNVALUE = NULL;
besEND

[John Spikowski]

I solved my SDL clipping issues.

' ScriptBasic GFX - Alpha Circles

IMPORT gfx.inc

gfx::Window 640, 480, "ScriptBasic GFX - Alpha Circles"
' Random Value Arrays
RANDOMIZE(gfx::Time())
FOR i = 0 TO 512
  rx[i] = RND() % 640
  ry[i] = 60 + RND() % 480 - 80
  rz[i] = RND() % 64
  rr[i] = RND() AND  255
  rg[i] = RND() AND  255
  rb[i] = RND() AND  255
  af = rx[i] / 640
  ra[i] = INT(255 * af)
NEXT

ts = gfx::Time()
gfx::SDL_SetClipRect 0, 0, 640, 480
FOR i = 0 TO 512
  gfx::filledCircleRGBA rx[i], ry[i], rz[i], rr[i], rg[i], rb[i], ra[i]
NEXT
te = gfx::Time()
gfx::stringColor 20, 15,"Time: " & FORMAT("%.4f",(te-ts)/1000) & " Seconds." & CHR(0), 0xffffffff
gfx::Update
WHILE gfx::KeyName(1) <> "-escape"
WEND
gfx::Close