[OL] invisible bitmap handling

no-reply@allegro.cc (imaxcs) — Sun, 23 Jul 2006 19:27:45 +0000

Hi!

OpenLayer is a great library, but to me, it still has some quirks which make it unusable for some tasks. On of them has to do with the handling of invisible bitmaps. Please have a look at the following code:

1#include "tilechunkrendertest.h"
2 
3void save_screenshot(const char *path)
4{
5  BITMAP *bmp = create_bitmap(SCREEN_W,SCREEN_H);
6  if(!bmp) return;
7  unsigned char *buff = new unsigned char[4*SCREEN_W*SCREEN_H];
8  if(!buff)
9  {
10    destroy_bitmap(bmp);
11    return;
12  }
13 
14  glReadPixels(0,0,SCREEN_W,SCREEN_H,GL_RGBA,GL_UNSIGNED_BYTE,buff);
15 
16  int y;
17  for(y=0;y<SCREEN_H;y++)
18    memcpy(bmp->line[y],buff+4*SCREEN_W*(SCREEN_H-1-y),4*SCREEN_W);
19 
20  save_bitmap(path,bmp,NULL);
21 
22  destroy_bitmap(bmp);
23  delete buff;
24}
25 
26 
27int main(void)
28{
29  Setup::SetupProgram();
30 
31  Settings::StoreMemoryBitmaps(true);
32 
33  Setup::SetupScreen(800, 600, WINDOWED);
34 
35  set_color_depth(32);
36 
37  Settings::SetAntialiasing(true);
38 
39  Bitmap test(200, 200, Rgba::INVISIBLE);
40 
41  Canvas::SetTo(test);
42  Rect(90, 90, 20, 20).Draw(Rgba::RED);
43 
44  Canvas::SetTo(SCREEN_BACKBUF);
45  Canvas::Fill(Rgba::BLUE);
46 
47  test.Blit(100, 100);
48 
49  Canvas::Refresh();
50 
51  save_screenshot("out.bmp");
52 
53  return 0;
54}

(I omit the .h-file because it just includes the necessary headers)
Now, IMO, the bitmap it produces should look like the first attached picture (out_right.gif). But it looks like the second (out_wrong.gif).
It seems like when you draw to a bitmap, all invisible areas get filled with black, which is not a wanted behavior.

Why is that? Is there even a way to create these kind of bitmaps in Openlayer?

I need it for my game-project (the current IOTD, btw ), because right now, I render all tiles separately. But I want to create larger tile-chunks when the map loads to reduce the number of renders. (rendering a few big bitmaps is faster than more small bitmaps). For, example, I want to always group 5x5 tiles into one bitmap.

Thanks for your help!

no-reply@allegro.cc (Richard Phipps) — Sun, 23 Jul 2006 19:31:37 +0000

Try adding this:

 // Deal with cases where people have a screen with an alpha channel.
 Canvas::SetPixelWriteMode( COLOR_AND_ALPHA );

After your settings::SetAntiAliasing(true) line.

no-reply@allegro.cc (imaxcs) — Sun, 23 Jul 2006 19:39:53 +0000

Didn't work. Still produces the same output.

no-reply@allegro.cc (Richard Phipps) — Sun, 23 Jul 2006 19:49:45 +0000

Not sure if the created bitmap has an alpha channel.
Does:

if( test.HasAlphaChannel() ) {
  allegro_message( "Yes it does!" );
}

Show the message?

no-reply@allegro.cc (imaxcs) — Sun, 23 Jul 2006 19:57:17 +0000

Yes it does!

edit: Did you try the code yourself? What do you get?

no-reply@allegro.cc (Richard Phipps) — Sun, 23 Jul 2006 20:02:36 +0000

No, I haven't compiled the code.

Does adding this make any difference before blitting?
Blenders::Set( ALPHA_BLENDER );
It shouldn't do, but just checking..

no-reply@allegro.cc (imaxcs) — Sun, 23 Jul 2006 20:13:26 +0000

You are right! It doesn't change anything...:(

But, nevertheless, I really appreciate your help, Richard! Thanks a lot!

no-reply@allegro.cc (Richard Phipps) — Sun, 23 Jul 2006 21:08:50 +0000

Imaxcs, I made a new project, cut out your code and made it draw to the screen until I pressed the mouse. It works fine for me. If I change the INVISIBLE to BLACK I get the black square too.

Are you sure your screenshot save function is not causing the problem? Do you see the output on the screen?

Finally, what version of OpenLayer are you using? I use 2.0

no-reply@allegro.cc (Fladimir da Gorf) — Mon, 24 Jul 2006 00:46:41 +0000

Quote:

It seems like when you draw to a bitmap, all invisible areas get filled with black, which is not a wanted behavior.

You should use the latest SVN version.

no-reply@allegro.cc (imaxcs) — Mon, 24 Jul 2006 01:23:52 +0000

Quote:

Are you sure your screenshot save function is not causing the problem? Do you see the output on the screen?

No, my screenshot-function surely does work right. I can see the black square on the screen too.

Quote:

Finally, what version of OpenLayer are you using? I use 2.0

Quote:

You should use the latest SVN version.

I am using an SVN-version which is about 1 month old. Has anything changed since then?

Anyway, I use Gentoo Linux. Could it be the case that this doesn't work because of that? And I have a Nvidia Geforce MX 440 Go. Maybe that's it?

no-reply@allegro.cc (Richard Phipps) — Mon, 24 Jul 2006 02:43:12 +0000

I'm not using a newish SVN version and I have a Geforce 4 MX 440SE.

Any more ideas Flad?

no-reply@allegro.cc (imaxcs) — Mon, 24 Jul 2006 13:37:15 +0000

Here is an even shorter version, which uses OL's save-function to create the screenshot:

1#include "tilechunkrendertest.h"
2 
3int main(void)
4{
5  Setup::SetupProgram();
6 
7  Settings::StoreMemoryBitmaps(true);
8 
9  Setup::SetupScreen(800, 600, WINDOWED);
10 
11  set_color_depth(32);
12 
13  Settings::SetAntialiasing(true);
14 
15  Bitmap test(200, 200, Rgba::INVISIBLE);
16 
17  Canvas::SetTo(test);
18  Rect(90, 90, 20, 20).Draw(Rgba::RED);
19 
20  Canvas::SetTo(SCREEN_BACKBUF);
21  Canvas::Fill(Rgba::BLUE);
22 
23  test.Blit(100, 100);
24 
25  Canvas::Refresh();
26 
27  Canvas::Save( "out.png" );
28 
29  return 0;
30}

Still, it doesn't work!
I will try it under Windows...

no-reply@allegro.cc (Richard Phipps) — Mon, 24 Jul 2006 13:41:35 +0000

Well the old code works for me, so it sounds like it's either something in OpenLayer, AllegroGL or your gfx drivers. Does it work in full screen?

BTW: I don't think you need the set-color-depth(32) line. Does it make a difference if you remove it?

no-reply@allegro.cc (imaxcs) — Mon, 24 Jul 2006 13:58:26 +0000

Quote:

Does it work in full screen?

Quote:

BTW: I don't think you need the set-color-depth(32) line. Does it make a difference if you remove it?

No, that doesn't change anything...

Quote:

Well the old code works for me, so it sounds like it's either something in OpenLayer, AllegroGL or your gfx drivers.

I just tried it under Windows and it worked. So the problem is Linux. It seems to handle these bitmaps a bit different. Flad?

no-reply@allegro.cc (Fladimir da Gorf) — Mon, 24 Jul 2006 15:20:10 +0000

Maybe it's the OpenGL drivers then... But I'll check if there's an issue with the alpha channels...

no-reply@allegro.cc (imaxcs) — Wed, 26 Jul 2006 17:49:16 +0000

Did you find something?

1	#include "tilechunkrendertest.h"
2
3	void save_screenshot(const char *path)
4	{
5	BITMAP *bmp = create_bitmap(SCREEN_W,SCREEN_H);
6	if(!bmp) return;
7	unsigned char buff = new unsigned char[4SCREEN_W*SCREEN_H];
8	if(!buff)
9	{
10	destroy_bitmap(bmp);
11	return;
12	}
13
14	glReadPixels(0,0,SCREEN_W,SCREEN_H,GL_RGBA,GL_UNSIGNED_BYTE,buff);
15
16	int y;
17	for(y=0;y<SCREEN_H;y++)
18	memcpy(bmp->line[y],buff+4SCREEN_W(SCREEN_H-1-y),4*SCREEN_W);
19
20	save_bitmap(path,bmp,NULL);
21
22	destroy_bitmap(bmp);
23	delete buff;
24	}
25
26
27	int main(void)
28	{
29	Setup::SetupProgram();
30
31	Settings::StoreMemoryBitmaps(true);
32
33	Setup::SetupScreen(800, 600, WINDOWED);
34
35	set_color_depth(32);
36
37	Settings::SetAntialiasing(true);
38
39	Bitmap test(200, 200, Rgba::INVISIBLE);
40
41	Canvas::SetTo(test);
42	Rect(90, 90, 20, 20).Draw(Rgba::RED);
43
44	Canvas::SetTo(SCREEN_BACKBUF);
45	Canvas::Fill(Rgba::BLUE);
46
47	test.Blit(100, 100);
48
49	Canvas::Refresh();
50
51	save_screenshot("out.bmp");
52
53	return 0;
54	}