NAME¶
al_set_target_bitmap - Allegro 5 API
SYNOPSIS¶
-
#include <allegro5/allegro.h>
void al_set_target_bitmap(ALLEGRO_BITMAP *bitmap)
DESCRIPTION¶
This function selects the bitmap to which all subsequent drawing operations in
the calling thread will draw to. To return to drawing to a display, set the
backbuffer of the display as the target bitmap, using
al_get_backbuffer(3alleg5). As a convenience, you may also use
al_set_target_backbuffer(3alleg5).
Each video bitmap is tied to a display. When a video bitmap is set to as the
target bitmap, the display that the bitmap belongs to is automatically made
"current" for the calling thread (if it is not current already).
Then drawing other bitmaps which are tied to the same display can be hardware
accelerated.
A single display cannot be current for multiple threads simultaneously. If you
need to release a display, so it is not current for the calling thread, call
al_set_target_bitmap(NULL);
Setting a memory bitmap as the target bitmap will not change which display is
current for the calling thread.
OpenGL note:
Framebuffer objects (FBOs) allow OpenGL to directly draw to a bitmap, which is
very fast. When using an OpenGL display, if all of the following conditions
are met an FBO will be created for use with the bitmap:
- •
- The GL_EXT_framebuffer_object OpenGL extension is available.
- •
- The bitmap is not a memory bitmap.
- •
- The bitmap is not currently locked.
In Allegro 5.0.0, you had to be careful as an FBO would be kept around until the
bitmap is destroyed or you explicitly called al_remove_opengl_fbo(3alleg5) on
the bitmap, wasting resources. In newer versions, FBOs will be freed
automatically when the bitmap is no longer the target bitmap,
unless
you have called al_get_opengl_fbo(3alleg5) to retrieve the FBO id.
In the following example, no FBO will be created:
-
lock = al_lock_bitmap(bitmap);
al_set_target_bitmap(bitmap);
al_put_pixel(x, y, color);
al_unlock_bitmap(bitmap);
The above allows using al_put_pixel(3alleg5) on a locked bitmap without creating
an FBO.
In this example an FBO is created however:
-
al_set_target_bitmap(bitmap);
al_draw_line(x1, y1, x2, y2, color, 0);
An OpenGL command will be used to directly draw the line into the bitmap's
associated texture.
SEE ALSO¶
al_get_target_bitmap(3alleg5), al_set_target_backbuffer(3alleg5)