[A5] how to use a bitmap as a pattern to fill a rectangular area?

no-reply@allegro.cc (axilmar) — Thu, 30 Jan 2014 19:52:46 +0000

Hi, I'd like to fill a rectangular area with a bitmap used as a pattern. How do I do that with A5?

no-reply@allegro.cc (Don Freeman) — Thu, 30 Jan 2014 20:29:50 +0000

Use the primitives addon. Look at the source code for the primitives example...

no-reply@allegro.cc (axilmar) — Thu, 30 Jan 2014 21:19:11 +0000

Thanks. After lots of experimentation, I came up with this:

#SelectExpand
  1void al_draw_bitmap_rect(ALLEGRO_BITMAP *bmp, int sx, int sy, int sw, int sh, float dx, float dy, float dw, float dh, int flags) {
  ALLEGRO_BITMAP *sub = al_create_sub_bitmap(bmp, sx, sy, sw, sh);
  ALLEGRO_BITMAP *clone = al_clone_bitmap(sub);
  4
  ALLEGRO_COLOR c = al_map_rgb(255, 255, 255);
  6
  ALLEGRO_VERTEX vertices[4];
  8
  vertices[0].x = dx;
  vertices[0].y = dy;
  vertices[0].z = 0;
  vertices[0].color = c;
  vertices[0].u = 0;
  vertices[0].v = 0;
 15
  vertices[1].x = dx + dw;
  vertices[1].y = dy;
  vertices[1].z = 0;
  vertices[1].color = c;
  vertices[1].u = dw;
  vertices[1].v = 0;
 22
  vertices[2].x = dx;
  vertices[2].y = dy + dh;
  vertices[2].z = 0;
  vertices[2].color = c;
  vertices[2].u = 0;
  vertices[2].v = dh;
 29
  vertices[3].x = dx + dw;
  vertices[3].y = dy + dh;
  vertices[3].z = 0;
  vertices[3].color = c;
  vertices[3].u = dw;
  vertices[3].v = dh;
 36
  al_draw_prim(vertices, nullptr, clone, 0, 4, ALLEGRO_PRIM_TRIANGLE_STRIP);
 38
  al_destroy_bitmap(clone);
  al_destroy_bitmap(sub);
 41}

Am I doing it correctly? the visual output seems correct.

The function obviously creates and destroys bitmaps, so it's not the fastest thing. Other than pre-creating the bitmaps, is there another way to specify a subarea of the bitmap? perhaps using the vertices?

no-reply@allegro.cc (SiegeLord) — Fri, 31 Jan 2014 02:58:33 +0000

axilmar said:

Other than pre-creating the bitmaps, is there another way to specify a subarea of the bitmap? perhaps using the vertices?

Can't be done without shaders, which is why Allegro doesn't support this operation.

no-reply@allegro.cc (axilmar) — Fri, 31 Jan 2014 16:31:43 +0000

SiegeLord said:

Can't be done without shaders, which is why Allegro doesn't support this operation.

Thanks. So it seems I would have to actually split the bitmap into other bitmaps.