[Mesa-dev] [PATCH V2 12/14] meta: Fix reading luminance texture as rgba in _mesa_meta_pbo_GetTexSubImage()

[Anuj Phogat]

On Wed, Jul 22, 2015 at 7:10 AM, Iago Toral <itoral at igalia.com> wrote:
> The problem here is that the _mesa_meta_BlitFramebuffer is not setting
> G/B channels to 0.0 when doing Luminance/Intensity to RGBA conversions,
> so why not implement the fix in _mesa_meta_BlitFramebuffer directly? The
> GL spec expects frambuffer blits to handle these conversions properly,
> so it looks like a win for all uses of that function.
>
I couldn't find an OpenGL spec reference suggesting this conversion in case
of glBlitFrameBuffer.

What I found supports the current behavior of glBlitFrameBuffer:
See table 3.23 on page 220 (of pdf) of glspec30.20080811.

Some relevant text from https://www.opengl.org/wiki/Image_Format:
"When a GL_RED format is sampled in a shader, the resulting vec4 is
 (Red, 0, 0, 1). When a GL_INTENSITY format is sampled, the resulting
  vec4 is (I, I, I, I). The single intensity value is read into all four
  components. For GL_LUMINANCE, the result is (L, L, L, 1). There is
  also a two-channel GL_LUMINANCE_ALPHA format, which gives
  (L, L, L, A)."

I think glBlitFrameBuffer should also follow this being a drawing operation.
What do you think?

> Iago
>
> On Fri, 2015-07-17 at 10:28 -0700, Anuj Phogat wrote:
>> After recent addition of pbo testing in piglit test getteximage-luminance,
>> it fails on i965. This patch makes a sub test pass.
>>
>> This patch adds a clear color operation to meta pbo path, which I think is
>> better than falling back to software path.
>>
>> V2: Fix color mask for GL_LUMINANCE_ALPHA
>>
>> Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
>> Cc: <mesa-stable at lists.freedesktop.org>
>> ---
>>  src/mesa/drivers/common/meta_tex_subimage.c | 36 +++++++++++++++++++++++++++--
>>  1 file changed, 34 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/drivers/common/meta_tex_subimage.c b/src/mesa/drivers/common/meta_tex_subimage.c
>> index 13f8292..f4d5ac3 100644
>> --- a/src/mesa/drivers/common/meta_tex_subimage.c
>> +++ b/src/mesa/drivers/common/meta_tex_subimage.c
>> @@ -28,6 +28,7 @@
>>  #include "blend.h"
>>  #include "bufferobj.h"
>>  #include "buffers.h"
>> +#include "clear.h"
>>  #include "fbobject.h"
>>  #include "glformats.h"
>>  #include "glheader.h"
>> @@ -278,8 +279,9 @@ _mesa_meta_pbo_GetTexSubImage(struct gl_context *ctx, GLuint dims,
>>     int full_height, image_height;
>>     struct gl_texture_image *pbo_tex_image;
>>     struct gl_renderbuffer *rb = NULL;
>> -   GLenum status;
>> -   bool success = false;
>> +   GLenum status, src_base_format;
>> +   bool success = false, clear_channels_to_zero = false;
>> +   float save_clear_color[4];
>>     int z;
>>
>>     if (!_mesa_is_bufferobj(packing->BufferObj))
>> @@ -380,6 +382,27 @@ _mesa_meta_pbo_GetTexSubImage(struct gl_context *ctx, GLuint dims,
>>                                    GL_COLOR_BUFFER_BIT, GL_NEAREST))
>>        goto fail;
>>
>> +   src_base_format = tex_image ?
>> +                     tex_image->_BaseFormat :
>> +                     ctx->ReadBuffer->_ColorReadBuffer->_BaseFormat;
>> +
>> +   /* Depending on the base formats involved we might need to rebase some
>> +    * values. For example if we download from a Luminance format to RGBA
>> +    * format, we want G=0 and B=0.
>> +    */
>> +   clear_channels_to_zero =
>> +      _mesa_need_luminance_to_rgb_conversion(src_base_format,
>> +                                             pbo_tex_image->_BaseFormat);
>> +
>> +   if (clear_channels_to_zero) {
>> +      memcpy(save_clear_color, ctx->Color.ClearColor.f, 4 * sizeof(float));
>> +      /* Clear the Green, Blue channels. */
>> +      _mesa_ColorMask(GL_FALSE, GL_TRUE, GL_TRUE,
>> +                      src_base_format != GL_LUMINANCE_ALPHA);
>> +      _mesa_ClearColor(0.0, 0.0, 0.0, 1.0);
>> +      _mesa_Clear(GL_COLOR_BUFFER_BIT);
>> +   }
>> +
>>     for (z = 1; z < depth; z++) {
>>        _mesa_meta_bind_fbo_image(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
>>                                  tex_image, zoffset + z);
>> @@ -392,6 +415,15 @@ _mesa_meta_pbo_GetTexSubImage(struct gl_context *ctx, GLuint dims,
>>                                   0, z * image_height,
>>                                   width, z * image_height + height,
>>                                   GL_COLOR_BUFFER_BIT, GL_NEAREST);
>> +      if (clear_channels_to_zero)
>> +         _mesa_Clear(GL_COLOR_BUFFER_BIT);
>> +   }
>> +
>> +   /* Unmask the color channels and restore the saved clear color values. */
>> +   if (clear_channels_to_zero) {
>> +      _mesa_ColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
>> +      _mesa_ClearColor(save_clear_color[0], save_clear_color[1],
>> +                       save_clear_color[2], save_clear_color[3]);
>>     }
>>
>>     success = true;
>
>