[a5] filtering primitives for offscreen bitmaps?

no-reply@allegro.cc (Mark Oates) — Wed, 09 Jun 2010 07:30:16 +0000

Hey again.

When drawing primitives to a bitmap other than the backbuffer, the multisampling fails. In this example, I've drawn a line to the backbuffer (on the left), and also drawn it to an offscreen bitmap (right)

#SelectExpand
  1ALLEGRO_BITMAP *offscreen_render;
  2
  3// initialize code
  4
  5offscreen_render = al_create_bitmap(200, 150);
  6
  7// in the draw code
  8
  9   al_set_target_bitmap(offscreen_render);
 10   al_clear_to_color(color("light green"));
 11   al_draw_line(10, 120, 190, 100, color("red"), 3);
 12
 13   al_set_target_bitmap(al_get_backbuffer());
 14   al_draw_line(10, 120, 190, 100, color("red"), 3);
 15
 16   al_draw_bitmap(offscreen_render, 200, NULL);

Produces:
{"name":"601549","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/4\/d489f234eb978a284c3b80a3ca50963f.png","w":442,"h":217,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/4\/d489f234eb978a284c3b80a3ca50963f"}

I tried adding the al_set_new_bitmap_flags(ALLEGRO_VIDEO_BITMAP) before creating the bitmap to be sure, but it didn't change anything. My idea for a workaround is to prerender onto the backbuffer and draw from there to intended prerender location. This doesn't seem ideal but it could work.

[edit] oops, topic should be "[a5] multisampling primitives for offscreen bitmaps?"

[edit] I've tried drawing with the backbuffer to another surface but it won't permit it. The console outputs 'fail'.

no-reply@allegro.cc (Elias) — Wed, 09 Jun 2010 18:46:47 +0000

Yes, multi-sampling is only supported on the display backbuffer so far (with OpenGL at least).

I wouldn't know how to enable multi-sampling for an FBO. If there's some simple OpenGL setting for it we should enable it.

Otherwise, need a patch to implement it.

Do you know if it works with DirectX?

no-reply@allegro.cc (Milan Mimica) — Wed, 09 Jun 2010 20:12:30 +0000

EXT_framebuffer_multisample looks like it.

no-reply@allegro.cc (Elias) — Wed, 09 Jun 2010 20:35:32 +0000

Quote:

No method is provided for creating multisample texture images.

Since we only support drawing into bitmaps (textures) and have no actual "off-screen" buffers, does this mean we cannot use it?

no-reply@allegro.cc (Mark Oates) — Thu, 10 Jun 2010 04:13:18 +0000

Elias said:

Do you know if it works with DirectX?

No. It does not work with DirectX.