Certain tests (e.g. piglit's crossbar) crash because they do (possibly
somewhat weird things) with glReadBuffer().
What happens is this:
- Context gets set up, made current
- Stuff gets rendered
- glReadBuffer() is called to change the read buffer
- glReadPixels() crashes because now ctx->ReadBuffer->_ColorReadBuffer has no
corresponding buffer object
The issue is that the front buffer's buffer object is never opened. Buffer
objects for renderbuffers are opened in radeon_update_renderbuffers(), but the
front buffer buffer object is only opened if we are in single-buffer mode or
rendering to the front buffer. This just seems incorrect, since clearly *read*
and *draw* buffer may be different.
On the other hand, there was probably a reason to put this check there in the
first place, and I would like to understand that reason before blindly
changing the code. Can somebody enlighten me?
In the meantime, the attached patch fixes the crash for me.
cu,
Nicolai
diff --git a/src/mesa/drivers/dri/radeon/radeon_common_context.c b/src/mesa/drivers/dri/radeon/radeon_common_context.c
index eb0e5b3..009859f 100644
--- a/src/mesa/drivers/dri/radeon/radeon_common_context.c
+++ b/src/mesa/drivers/dri/radeon/radeon_common_context.c
@@ -487,8 +487,7 @@ radeon_update_renderbuffers(__DRIcontext *context, __DRIdrawable *drawable)
struct radeon_renderbuffer *stencil_rb;
i = 0;
- if ((radeon->is_front_buffer_rendering || !draw->color_rb[1])
- && draw->color_rb[0]) {
+ if (draw->color_rb[0]) {
attachments[i++] = __DRI_BUFFER_FRONT_LEFT;
attachments[i++] = radeon_bits_per_pixel(draw->color_rb[0]);
}
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