|
Help with understanding bitmap locking |
jmasterx
Member #11,410
October 2009
|
Essentially I want to lock the bitmap and get the alpha component of each pixel. I have the following code: //lock the bitmap ALLEGRO_LOCKED_REGION* region; region = al_lock_bitmap (m_bitmap, ALLEGRO_PIXEL_FORMAT_ABGR_8888, ALLEGRO_LOCK_READONLY); for(int y = 0; y < m_bitmapDimensions.y; ++y) { for(int x = 0; x < m_bitmapDimensions.x; ++x) { } } But after that I'm stuck. I'm not sure how to get the 32 bit integer representing the color components, and then I'm unsure how the logical shifts work to extract the alpha in an endian independent way. Thanks Agui GUI API -> https://github.com/jmasterx/Agui |
Elias
Member #358
May 2000
|
ALLEGRO_LOCKED_REGION* region; region = al_lock_bitmap(bitmap, ALLEGRO_PIXEL_FORMAT_ABGR_8888, ALLEGRO_LOCK_READONLY); for(int y = 0; y < al_get_bitmap_height(bitmap); ++y) { unsigned char *row = region->data; row += y * region->pitch; uint32_t *pixel = row; for(int x = 0; x < al_get_bitmap_width(bitmap); ++x) { int alpha = *pixel >> 24; /* do something with alpha */ pixel++; } } al_unlock_bitmap(bitmap);
[edit:] ALLEGRO_LOCKED_REGION* region; region = al_lock_bitmap(bitmap, ALLEGRO_PIXEL_FORMAT_ABGR_8888_LE, ALLEGRO_LOCK_READONLY); for(int y = 0; y < al_get_bitmap_height(bitmap); ++y) { unsigned char *pixel = region->data; pixel += y * region->pitch; for(int x = 0; x < al_get_bitmap_width(bitmap); ++x) { pixel += 3; int alpha = *pixel; /* do something with alpha */ pixel++; } } al_unlock_bitmap(bitmap); Both solution are endian independent (not that you will still find a lot of big endian hardware). -- |
Matthew Leverton
Supreme Loser
January 1999
|
uint32_t *p = lock->data; int a; for each pixel: a = p[x] >> 24 at end of row: p += lock->pitch;
|
jmasterx
Member #11,410
October 2009
|
Thank you to both of you Agui GUI API -> https://github.com/jmasterx/Agui |
|