Thanks for pointing that out, Chris.  I had forgotten about that language.

This test came about after fixing a bug in our driver when running the game Flockers, from Steam. It has a few vertex arrays with unusual layout. I'll have to go back and double-check the data type. Maybe it was ubyte instead of float...

-Brian

On 06/21/2015 03:41 AM, Chris Forbes wrote:
Jose,

I believe that's exactly what it's saying, yes.

- Chris

On Sun, Jun 21, 2015 at 8:00 PM, Jose Fonseca <[email protected]> wrote:
It depends on the platform.  But x86 doesn't require floats to be 4-byte aligned. 
https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Data-5Fstructure-5Falignment-23x86&d=BQIBaQ&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw-YihVMNtXt-uEs&r=T0t4QG7chq2ZwJo6wilkFznRSFy-8uDKartPGbomVj8&m=hoZapaHEiAtCP0Hl8wUx6-p35QL0Xat2wQTeFYWssvk&s=udFG-s3z0zheKxzbzEgjB4bmtZ0DLIn3FVJLIpf8L2E&e=

I don't know about other platforms though -- it might be indeed necessary to 
skip or be less strict on non-x86 platforms.

I'm having trouble interpreting the "additional base-level requirement" means. 
Is it saying that a an offset to a float (4bytes), must be 4bytes aligned, regardless the 
platform can deal with non- 4-byte aligned floats?

Jose

________________________________________
From: Piglit <[email protected]> on behalf of Chris Forbes 
<[email protected]>
Sent: 20 June 2015 11:32
To: Brian Paul
Cc: [email protected]
Subject: Re: [Piglit] [PATCH] gl-1.5-vertex-buffer-offsets: test unusual vertex 
offsets/strides

Brian,

Doesn't this test run afoul of the alignment requirements?

The OpenGL 1.5 specification, page 33 [first version in which this is
introduced;
equivalent language exists in later spec versions] says:

   "Clients must align data elements consistent with the requirements of the
   client platform, with an additional base-level requirement that an
offset within
   a buffer to a datum comprising N basic machine units be a multiple of N."

Non-naturally-aligned float attributes sourced from a buffer object would appear
to violate this rule - or have I misunderstood?

- Chris




On Sat, Jun 20, 2015 at 2:39 AM, Brian Paul <[email protected]> wrote:
The draw-vertices tests exercises unusual vertex sizes and strides,
but not with interleaved arrays.

This test creates a VBO with interleaved vertex positions and colors.
The colors are positioned at offsets like 9, 10 and 11 bytes from the
start of the vertex.  Unusual strides between vertices are tested too.

Exercises a bug in Gallium's u_vbuf code where the driver was passed
pipe_vertex_element::src_offset values which weren't a multiple of
four, even when PIPE_CAP_VERTEX_ELEMENT_SRC_OFFSET_4BYTE_ALIGNED_ONLY
returned 1.
---
  tests/all.py                              |   1 +
  tests/spec/gl-1.5/CMakeLists.gl.txt       |   1 +
  tests/spec/gl-1.5/vertex-buffer-offsets.c | 124 ++++++++++++++++++++++++++++++
  3 files changed, 126 insertions(+)
  create mode 100644 tests/spec/gl-1.5/vertex-buffer-offsets.c

diff --git a/tests/all.py b/tests/all.py
index ad4c494..ee11be6 100755
--- a/tests/all.py
+++ b/tests/all.py
@@ -1042,6 +1042,7 @@ with profile.group_manager(
        'normal3b3s-invariance-byte', run_concurrent=False)
      g(['gl-1.5-normal3b3s-invariance', 'GL_SHORT'],
        'normal3b3s-invariance-short', run_concurrent=False)
+    g(['gl-1.5-vertex-buffer-offsets'], 'vertex-buffer-offsets')

  with profile.group_manager(
          PiglitGLTest,
diff --git a/tests/spec/gl-1.5/CMakeLists.gl.txt 
b/tests/spec/gl-1.5/CMakeLists.gl.txt
index 8dcd95d..f10c6cb 100644
--- a/tests/spec/gl-1.5/CMakeLists.gl.txt
+++ b/tests/spec/gl-1.5/CMakeLists.gl.txt
@@ -10,5 +10,6 @@ link_libraries (
  )

  piglit_add_executable (gl-1.5-normal3b3s-invariance normal3b3s-invariance.c)
+piglit_add_executable (gl-1.5-vertex-buffer-offsets vertex-buffer-offsets.c)

  # vim: ft=cmake:
diff --git a/tests/spec/gl-1.5/vertex-buffer-offsets.c 
b/tests/spec/gl-1.5/vertex-buffer-offsets.c
new file mode 100644
index 0000000..6d58331
--- /dev/null
+++ b/tests/spec/gl-1.5/vertex-buffer-offsets.c
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2015  VMware, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * Test interleaved vertex arrays with unusual element offsets and strides.
+ * Brian Paul
+ */
+
+#include "piglit-util-gl.h"
+
+PIGLIT_GL_TEST_CONFIG_BEGIN
+       config.supports_gl_compat_version = 15;
+       config.window_visual = PIGLIT_GL_VISUAL_RGBA | PIGLIT_GL_VISUAL_DOUBLE;
+PIGLIT_GL_TEST_CONFIG_END
+
+
+void
+piglit_init(int argc, char **argv)
+{
+       /* nothing */
+}
+
+
+static bool
+test_offset_stride(int color_offset, int stride)
+{
+       static const GLfloat vertex[4][2] = {
+               { -1, -1 },
+               {  1, -1 },
+               {  1,  1 },
+               { -1,  1 }
+       };
+       static const GLfloat color[4] = { 0.0, 1.0, 0.5, 1.0 };
+       GLubyte buffer[1000];
+       GLuint buf;
+       int i, pos;
+       bool p;
+
+       assert(color_offset >= sizeof(vertex[0]));
+       assert(stride >= color_offset + sizeof(color));
+
+       pos = 0;
+       for (i = 0; i < 4; i++) {
+               /* copy vertex position into buffer */
+               memcpy(buffer + pos, vertex[i], sizeof(vertex[i]));
+
+               /* copy vertex color into buffer at unusual offset */
+               memcpy(buffer + pos + color_offset, color, sizeof(color));
+
+               pos += stride;
+       }
+       assert(pos <= sizeof(buffer));
+
+       glGenBuffers(1, &buf);
+       glBindBuffer(GL_ARRAY_BUFFER, buf);
+       glBufferData(GL_ARRAY_BUFFER, sizeof(buffer),
+                                        buffer, GL_STATIC_DRAW);
+
+       glVertexPointer(2, GL_FLOAT, stride, (void *) 0);
+       glColorPointer(4, GL_FLOAT, stride, (void *) (size_t) color_offset);
+       glEnable(GL_VERTEX_ARRAY);
+       glEnable(GL_COLOR_ARRAY);
+
+       glClear(GL_COLOR_BUFFER_BIT);
+       glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+
+       p = piglit_probe_rect_rgba(0, 0, piglit_width, piglit_height, color);
+
+       if (!p) {
+               printf("failure for color_offset %d, stride %d\n",
+                      color_offset, stride);
+       }
+
+       piglit_present_results();
+
+       glDeleteBuffers(1, &buf);
+
+       return p;
+}
+
+
+enum piglit_result
+piglit_display(void)
+{
+       bool pass = true;
+
+       /* test nice values */
+       pass = test_offset_stride(8, 24) && pass;
+       pass = test_offset_stride(12, 28) && pass;
+
+       /* test unual offset */
+       pass = test_offset_stride(9, 32) && pass;
+
+       /* test unual stride */
+       pass = test_offset_stride(8, 27) && pass;
+
+       /* test unusual offset, unusual stride */
+       pass = test_offset_stride(9, 25) && pass;
+       pass = test_offset_stride(10, 26) && pass;
+       pass = test_offset_stride(11, 27) && pass;
+
+       return pass ? PIGLIT_PASS : PIGLIT_FAIL;
+}
+
--
1.9.1

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