ALLEGRO 5 - Bitmap Corruption after writing to source image

Kev Callahan

I'm currently messing around with ALLEGRO 5 on an ARM chip (iMX6).
I pretty much seem to have it running but a weird issue has now arisen.

I found this initially whilst using al_convert_mask_to_alpha() converting magic pink to transparency.

The issue is that if I have an ALLEGRO_BITMAP and drawing it straight to the display everything's fine.

However if I write to this BITMAP using al_convert_mask_to_alpha() or even if I draw another smaller BITMAP onto it, then it appears to corrupt the original image.

Setting a single pixel on the image doesn't appear to have any corruption effect..

Any ideas on how I best investigate this to track down the error?
I'm suspicious that maybe it's a colour depth issue (could it change?) but am struggling where to go from here..!

EDIT:
Okay more information.

bmp1 is 200x200
bmp2 is 200x200
bmp3 is 20x20

Load bmp1 and leave as is - drawn okay on display.
Load bmp2 and leave as is - drawn okay on display
Load bmp2 and draw bmp3 on it - bmp3 'part' looks fine, rest of bmp2 is corrupt.
Now..
If I load bmp2, draw bmp3, then draw bmp1 onto it, it looks fine.
If I load bmp2, draw bmp3, then draw bmp1 onto it, then draw bmp3 onto it, it looks fine.
Aarrgh... Bitmap colour depth issue??

EDIT2:
It appears the smaller bitmap is 24 bit depth, the larger images are 32..
Shouldn't this sort itself out..?

Elias

Could also be a bug in OpenGL drivers - but more likely in Allegro. Can you post a minimal program reproducing it?

Kev Callahan

As requested (pardon the hastily stripped down source), also attached the two source images, screenshot showing corruption and allegro.log

tried with 24bit and 32 bit source images - same issue.
Could be OPENGL drivers as I'm using an embedded card using the Vivante GC2000 drivers..

Thanks.

#SelectExpand
   1#include <stdio.h>
   2#include <stdlib.h>
   3#include <math.h>
   4#include <signal.h>
   5#include <ctype.h>
   6
   7#include <allegro5/allegro.h>
   8#include <allegro5/allegro_image.h>
   9#include <allegro5/allegro_font.h>
  10#include <allegro5/allegro_ttf.h>
  11#include <allegro5/allegro_primitives.h>
  12#include <allegro5/allegro_opengl.h>
  13#include <allegro5/allegro_image.h>
  14
  15#include "header.h"
  16#include "font.h"
  17#include "button.h"
  18
  19int winsize_x = 640;
  20int winsize_y = 480;
  21
  22ALLEGRO_DISPLAY *display = NULL;
  23
  24#define HZTIMER  30
  25
  26ALLEGRO_BITMAP *bmp1, *bmp2, *bmp3;
  27
  28// **
  29int main(int argc, char **argv)
  30{
  31  int  drawpage=0, mouse_x=0, mouse_y=0;
  32  char inifile[32] = {0};
  33
  34  ALLEGRO_TIMER          *timer      = NULL;
  35  ALLEGRO_EVENT_QUEUE    *eventq     = NULL;
  36  ALLEGRO_KEYBOARD_STATE *kbdstate   = NULL;
  37  ALLEGRO_MOUSE_STATE    *mousestate = NULL;
  38
  39  // ** allegro initialisation
  40  {
  41    if (! al_init()) { fprintf(stderr, "Failed to initialise ALLEGRO\n"); return -1; }
  42
  43    // input
  44    if (! al_install_keyboard()) { WHERE(); }
  45    if (! al_install_mouse   ()) { WHERE(); }
  46
  47    // addons
  48    al_init_image_addon();
  49    al_init_font_addon();
  50    al_init_ttf_addon();
  51    al_init_primitives_addon();
  52  }
  53
  54  // ** create default path for resources
  55  {
  56    ALLEGRO_PATH *path = al_get_standard_path(ALLEGRO_RESOURCES_PATH);
  57    al_append_path_component(path, "resources");
  58    al_change_directory(al_path_cstr(path, '/'));
  59    fprintf(stderr, "PATH: %s\n", al_path_cstr(path, '/'));
  60    al_destroy_path(path);
  61  }
  62
  63  // ** setup display
  64  {
  65    al_set_new_display_flags (ALLEGRO_OPENGL);
  66    al_set_new_display_option(ALLEGRO_SAMPLE_BUFFERS, 1, ALLEGRO_SUGGEST);
  67    al_set_new_display_option(ALLEGRO_SAMPLES,        8, ALLEGRO_SUGGEST);
  68
  69    display = al_create_display(winsize_x, winsize_y);
  70
  71    printf("OPENGL VERSION %x\n", al_get_opengl_version());
  72    printf("OPENGL VARIANT %x\n", al_get_opengl_variant());
  73
  74    if (! display) { fprintf(stderr, "failed to create display %dx%d\n", winsize_x, winsize_y); return -1; }
  75
  76    fprintf(stderr, "Created Display %dx%d\n", winsize_x, winsize_y);
  77
  78    al_set_window_title(display, "SIMPLE");
  79  }
  80
  81  // clear display
  82  {
  83    al_set_target_backbuffer(display);
  84    al_clear_to_color(al_map_rgb(12,13,18));
  85  }
  86
  87  bmp1  = al_load_bitmap("200x200.png");
  88  bmp2  = al_load_bitmap("200x200.png");
  89  bmp3  = al_load_bitmap("20x20.png");
  90
  91  //al_convert_mask_to_alpha(bmp2, al_map_rgb(255,0,255)); // magic pink is transparent
  92
  93  // cause bug - draw bmp3 onto bmp2
  94  {
  95    al_set_target_bitmap(bmp2);
  96    al_draw_bitmap(bmp3, 50, 50, 0); 
  97  }
  98
  99  al_set_target_backbuffer(display);
 100
 101
 102  eventq = al_create_event_queue();
 103
 104  // ** loop
 105  while (1)
 106  {
 107    // ** draw on display
 108    {
 109      al_set_target_backbuffer(display);
 110      al_draw_bitmap(bmp1,   0,   0, 0);
 111      al_draw_bitmap(bmp2, 320,   0, 0);
 112    }
 113
 114    al_flip_display();
 115
 116  }
 117
 118  // ** shutdown
 119  {
 120    al_destroy_display(display);
 121  }
 122
 123  return 0;
 124}

EDIT:

Much more investigation today - I'm now thinking there are driver issues (maybe I need to do something like Trent did for the Raspberry Pi to get Allegro working on this card, but quite frankly that's beyond me).

To summarise, it appears that loading a bitmap and displaying on the screen appears to work, but as soon as I read or write access that bitmap (eg with al_get_pixel()), the image reverts to an 'old' version that's cached somewhere... (in the GPU?) from previously (demonstrated by changing the images used).
Is there any way I can 'invalidate' the bitmap[ stored in the GPU?
Must admit this isn't an area I wanted to investigate and my knowledge of this is pretty much zero.

Thread #615550. Printed from Allegro.cc