On 12/15/2012 01:27 PM, Paul Berry wrote:
On 14 December 2012 13:01, Paul Berry <stereotype...@gmail.com
<mailto:stereotype...@gmail.com>> wrote:
From the GL 4.3 spec, section 6.7.1 (Indexed Buffer Object Limits and
Binding Queries):
To query the starting offset or size of the range of a buffer
object binding in an indexed array, call GetInteger64i v with
target set to respectively the starting offset or binding size
name from table 6.5 for that array. index must be in the range
zero to the number of bind points supported minus one. If the
starting offset or size was not specified when the buffer object
was bound (e.g. if it was bound with BindBufferBase), or if no
buffer object is bound to the target array at index, zero is
returned.
Similar language exists in the EXT_transform_feedback spec and in the
GLES3 spec.
Previously, if a buffer object was bound by glBindBufferBase(), the
GL_TRANSFORM_FEEDBACK_BUFFER_SIZE query returned the size of the
buffer.
Fixes GLES3 conformance tests
transform_feedback_{builtin_type,state_variables}.test.
NAK this patch. After some more careful re-reading of the GL and GLES
specs, I believe it implements the wrong behaviour. I'm thinking in
particular of this text (the last two paragraphs of section 2.9.1 of the
GLES 3 spec):
"BindBufferBase binds the entire buffer, even when the size of the
buffer is changed after the binding is established. It is equivalent to
calling BindBufferRange with offset zero, while size is determined by
the size of the bound buffer at the time the binding is used.
"Regardless of the size specified with BindBufferRange, or indirectly
with BindBufferBase, the GL will never read or write beyond the end of a
bound buffer. In some cases this constraint may result in visibly
different behavior when a buffer overflow would otherwise result, such
as described for transform feedback operations in section 2.14.2."
In the context of transform feedback, I interpret the phrase "at the
time the binding is used" to mean "at the time BeginTransformFeedback is
called." Mesa's current behaviour isn't consistent with the above two
paragraphs: it records the size of the buffer at the time BindBufferBase
is called, which means that if the buffer is grown after it's bound (but
before it's used), the entire buffer won't be used. Worse yet, in the
absence of extra checking by the driver, if the buffer is shrunk after
it's bound, there's a danger of transform feedback results overflowing
past the end of the buffer.
I think your new interpretation is correct. Can we come up with a
piglit test that would expose the buffer-growth-after-bind bug? I'm
curious to see what other drivers do...
I'm working on a replacement patch.
---
src/mesa/main/get.c | 2 +-
src/mesa/main/mtypes.h | 7 +++++++
src/mesa/main/transformfeedback.c | 10 ++++++----
3 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/src/mesa/main/get.c b/src/mesa/main/get.c
index f3dbda2..2348486 100644
--- a/src/mesa/main/get.c
+++ b/src/mesa/main/get.c
@@ -1574,7 +1574,7 @@ find_value_indexed(const char *func, GLenum
pname, GLuint index, union value *v)
goto invalid_value;
if (!ctx->Extensions.EXT_transform_feedback)
goto invalid_enum;
- v->value_int64 =
ctx->TransformFeedback.CurrentObject->Size[index];
+ v->value_int64 =
ctx->TransformFeedback.CurrentObject->QuerySize[index];
return TYPE_INT64;
case GL_TRANSFORM_FEEDBACK_BUFFER_BINDING:
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 18ab2db..333b2c9 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -1827,6 +1827,13 @@ struct gl_transform_feedback_object
GLintptr Offset[MAX_FEEDBACK_BUFFERS];
/** Max data to put into dest buffer (in bytes) */
GLsizeiptr Size[MAX_FEEDBACK_BUFFERS];
+ /**
+ * Size that should be returned from
GL_TRANSFORM_FEEDBACK_BUFFER_SIZE
+ * queries. If the transform feedback buffer was set up with
+ * glBindBufferBase() or glBindBufferOffsetEXT(). If it was set
up with
+ * glBindBufferRange() it is equal to ActualSize.
+ */
+ GLsizeiptr QuerySize[MAX_FEEDBACK_BUFFERS];
};
diff --git a/src/mesa/main/transformfeedback.c
b/src/mesa/main/transformfeedback.c
index 7d500bc..092c343 100644
--- a/src/mesa/main/transformfeedback.c
+++ b/src/mesa/main/transformfeedback.c
@@ -383,7 +383,8 @@ _mesa_EndTransformFeedback(void)
static void
bind_buffer_range(struct gl_context *ctx, GLuint index,
struct gl_buffer_object *bufObj,
- GLintptr offset, GLsizeiptr size)
+ GLintptr offset, GLsizeiptr size,
+ GLsizeiptr query_size)
{
struct gl_transform_feedback_object *obj =
ctx->TransformFeedback.CurrentObject;
@@ -407,6 +408,7 @@ bind_buffer_range(struct gl_context *ctx, GLuint
index,
obj->Offset[index] = offset;
obj->Size[index] = size;
+ obj->QuerySize[index] = query_size;
}
@@ -450,7 +452,7 @@
_mesa_bind_buffer_range_transform_feedback(struct gl_context *ctx,
return;
}
- bind_buffer_range(ctx, index, bufObj, offset, size);
+ bind_buffer_range(ctx, index, bufObj, offset, size, size);
}
@@ -485,7 +487,7 @@ _mesa_bind_buffer_base_transform_feedback(struct
gl_context *ctx,
*/
size = bufObj->Size & ~0x3;
- bind_buffer_range(ctx, index, bufObj, 0, size);
+ bind_buffer_range(ctx, index, bufObj, 0, size, 0);
}
@@ -546,7 +548,7 @@ _mesa_BindBufferOffsetEXT(GLenum target, GLuint
index, GLuint buffer,
*/
size = (bufObj->Size - offset) & ~0x3;
- bind_buffer_range(ctx, index, bufObj, offset, size);
+ bind_buffer_range(ctx, index, bufObj, offset, size, 0);
}
--
1.8.0.2
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