Locking bitmap is slower than not (?)

no-reply@allegro.cc (Ediolot) — Sun, 16 Oct 2016 22:35:14 +0000

Im trying to draw text and primitives to the screen.

This is my current drawing function:

#SelectExpand
  1
  2ALLEGRO_VERTEX *vertices;
  3
  4// ... calculate triangle points and save them to "vertices";
  5
  6al_clear_to_color(BACKGROUND_COLOR);
  7
  8al_lock_bitmap(al_get_target_bitmap(), ALLEGRO_PIXEL_FORMAT_ANY, 0); // The current target bitmap is the display back buffer
  9
 10al_draw_prim(vertices, null, null, 0, size, ALLEGRO_PRIM_TRIANGLE_LIST); // Draw triangles
 11al_draw_filled_rectangle(600, 0, 660, 660, al_map_rgb(255,255,255)); // Draw a rectangle
 12
 13al_unlock_bitmap(al_get_target_bitmap());
 14
 15al_draw_text(myfont, BLACK, 10, 10, ALLEGRO_ALIGN_LEFT, "TESTING");

When I draw around 180 000 triangles, Im getting 25FPS while locking the bitmap. But if I comment both the lock and unlock functions, Im getting ~60FPS !

I must be doing something terrible wrong with my drawing process (?). What's the correct order to draw and lock the bitmap ?.

Furthermore, why cant I clear the display with al_clear_to_color or write text to it when it is locked ?

Thanks a lot.

no-reply@allegro.cc (Edgar Reynaldo) — Mon, 17 Oct 2016 00:29:59 +0000

Short answer is, you don't need to lock the bitmap except for direct memory access, and you shouldn't.

The Manual : Graphics said:

Note: While a bitmap is locked, you can not use any drawing operations on it (with the sole exception of al_put_pixel and al_put_blended_pixel).

Basically, Allegro will lock the bitmap when it needs to, so you don't have to worry about it yourself, unless you're doing a lot of direct memory access.

no-reply@allegro.cc (beoran) — Mon, 17 Oct 2016 01:20:21 +0000

What you might be confusing locking the bitmap with is holding the bitmap drawing as per https://www.allegro.cc/manual/5/al_hold_bitmap_drawing. Locking is indeed only for direct access and hence, slows down drawing, but holding bitmap drawing can enhance performance if done right. Another way is to use possibly improve performance is the primitives functions.

no-reply@allegro.cc (Gideon Weems) — Mon, 17 Oct 2016 15:46:56 +0000

Here is a link for the discussion catcher (one of the cooleset, most under-rated features of these forums): al_hold_bitmap_drawing

no-reply@allegro.cc (Felix-The-Ghost) — Tue, 18 Oct 2016 11:53:03 +0000

Yep. I only lock bitmaps when I specifically use al_get_pixel or al_put_pixel