[Mesa-dev] [Mesa-users] Problem with ARB_copy_buffer on Mesa 9.2.4

[Benjamin Bellec]

Hello Jonas,

I tested your program and on my system (Fedora 19) on an Evergreen
(Radeon HD 5850) and I have the same issue indeed.
Here is my result :

Mesa 9.2.4 (from F19 repo) => Data does NOT match up!
Mesa 9.2.5 => Data does NOT match up!
Mesa 10.0.5 => Data does NOT match up!
Mesa 10.1.0 => Data matches.

So this is fixed in newer version.
That said, Mesa 9.2 is not supported anymore and I really don't know if
there will be a new Mesa 10.0.x release given the imminence of Mesa 10.2.
If yes, I can bisect and you can open a bug.

Mesa-dev, any new 10.0.x release planned ?

Regards.

Benjamin

Le 06/05/2014 13:40, Jonas Kulla a écrit :
> Hello list,
>
> after about 3 days of debugging, I was able to isolate a rather weird
> behavior in Mesa GL.
> The gist of it is the following: When I create a buffer object and
> allocate uninitilaized
> memory for it (glBufferData() with nullptr as 'data'),
> then glCopyBufferSubData() data into
> it from another buffer object, then subsequently fill a part of it
> with glBufferSubData(),
> this new data isn't visible to the buffer object. In fact, it seems
> that the SubData'ed bytes
> are completely lost. Any further data uploads however work as
> expected. I will attach
> a small C test case below that demonstrates this behavior.
>
> I realize that I am working with an old Mesa release (on Fedora 19),
> but I'm afraid of
> upgrading my system to the newest distro release as I might break my
> working environment.
> That's why I would like to kindly ask if someone could verify that
> this problem still persists
> on the newest Mesa code, in which case I would go ahead and file a bug
> report. At the
> same time, maybe someone could spot a critical mistake in my code that
> would explain
> this strange behavior I'm seeing. I think the code paths I'm hitting
> here in the driver are
> sufficiently obscure though.
>
> I should probably mention that my card is a Mobility Radeon HD 3650
> (ie. r600).
>
> Here's the code sample (you can replace the GL setup code with your own):
>
> #include <stdlib.h>
> #include <string.h>
>  
> #include <GL/glew.h>
> #include <SDL2/SDL.h>
>  
> static SDL_Window *win;
> static SDL_GLContext *ctx;
>  
> void setupGL()
> {
>         SDL_Init(SDL_INIT_VIDEO);
>         win = SDL_CreateWindow("CopyBufferBug",
> SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 64, 64,
> SDL_WINDOW_OPENGL);
>         ctx = SDL_GL_CreateContext(win);
>         glewInit();
> }
>  
> static void teardownGL()
> {
>         SDL_GL_DeleteContext(ctx);
>         SDL_DestroyWindow(win);
>  
>         SDL_Quit();
> }
>  
> int main(int argc, char *argv[])
> {
>         setupGL();
>  
>         /* These don't matter I think */
>         #define BLOCK_SIZE 128
>         #define BUFFER1_SIZE BLOCK_SIZE
>         #define BUFFER2_SIZE BLOCK_SIZE
>         #define BUFFER1_TARGET GL_COPY_READ_BUFFER
>         #define BUFFER2_TARGET GL_COPY_WRITE_BUFFER
>         #define BUFFER1_USAGE GL_DYNAMIC_DRAW
>         #define BUFFER2_USAGE GL_DYNAMIC_DRAW
>  
>         GLuint buffers[2];
>         glGenBuffers(2, buffers);
>  
>         /* We allocate both buffers with undefined memory */
>         glBindBuffer(BUFFER1_TARGET, buffers[0]);
>         glBufferData(BUFFER1_TARGET, BUFFER1_SIZE, 0, BUFFER1_USAGE);
>  
>         glBindBuffer(BUFFER2_TARGET, buffers[1]);
>         glBufferData(BUFFER2_TARGET, BUFFER2_SIZE, 0, BUFFER2_USAGE);
>  
>         /* Then copy (undefined) bytes from the first into the second
> buffer */
>         /* Note: If I comment this line out, everything works */
>         glCopyBufferSubData(BUFFER1_TARGET, BUFFER2_TARGET, 0, 0,
> BUFFER1_SIZE);
>  
>         /* Generate random string */
>         FILE *rand = fopen("/dev/urandom", "r");
>         char data[BLOCK_SIZE];
>         fread(data, 1, sizeof(data), rand);
>         fclose(rand);
>  
>         /* We fill the second buffer with defined data */
>         /* Note: If I execute this call twice (just copy paste the
> line), everything works */
>         glBufferSubData(BUFFER2_TARGET, 0, sizeof(data), data);
>  
>         /* Then download it again to compare its contents against our
> test string */
>         char data2[BLOCK_SIZE];
>         glGetBufferSubData(BUFFER2_TARGET, 0, sizeof(data2), data2);
>  
>         if (memcmp(data, data2, sizeof(data)))
>                 printf("Data does NOT match up!\n");
>         else
>                 printf("Data matches.\n");
>  
>         glDeleteBuffers(2, buffers);
>  
>         teardownGL();
>  
>         return 0;
> }
>
> Thank you very much for your time.
> Jonas
>
>
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> mesa-users at lists.freedesktop.org
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