[igt-dev] [PATCH i-g-t] tests/kms_plane_alpha_blend: Paint FBs with cairo source operator

[Kazlauskas, Nicholas]

On 2/22/19 12:39 PM, Ville Syrjälä wrote:
> On Fri, Feb 22, 2019 at 12:08:46PM -0500, Nicholas Kazlauskas wrote:
>> Cairo defaults to using a blended fill, so when IGT tries to paint on
>> top of a framebuffer in these tests with an alpha less than 1.0 the
>> previous framebuffer contents will still be present underneath.
>>
>> On amdgpu this is an issue because the framebuffer is created in
>> an unitialized state and can have contents from previous tests
>> still within memory.
> 
> igt_fb more or less assumes all fbs start out black. Sounds like you
> need a memset() or equivalent somewhere.

The buffer could also be painted to 0 implicitly using cairo. We also 
need a patch at some point to not generate the suspicious CRC read 
warning since our black screens are (0, 0, 0) and we rely on tests 
leaving garbage in the framebuffer to avoid it.

However, this patch would still be needed since the fill will still be 
blended by default. When creating transparent or semi-transparent 
buffers they should be filled in with the cairo source operator or the 
alpha channel won't be set to the correct value.

Nicholas Kazlauskas

> 
>>
>> This patch explicitly sets the cairo filling operator to SOURCE to
>> overwrite the contents when performing fills with alpha < 1.0 in
>> this test.
>>
>> It also fixes the creation of the transparent FB. My guess as for why
>> this test previously passed on i915 is because the primary FB was
>> also black, so the CRC would match even if the black overlay plane
>> was partially transparent.
>>
>> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>> ---
>>   tests/kms_plane_alpha_blend.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/tests/kms_plane_alpha_blend.c b/tests/kms_plane_alpha_blend.c
>> index 1d9d8933..d7dc44ab 100644
>> --- a/tests/kms_plane_alpha_blend.c
>> +++ b/tests/kms_plane_alpha_blend.c
>> @@ -83,6 +83,7 @@ static void draw_squares(struct igt_fb *fb, int w, int h, double a)
>>   {
>>   	cairo_t *cr = igt_get_cairo_ctx(fb->fd, fb);
>>   
>> +	cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
>>   	igt_paint_color_alpha(cr, 0, 0,         w / 2, h / 2, 1., 0., 0., a);
>>   	igt_paint_color_alpha(cr, w / 2, 0,     w / 2, h / 2, 0., 1., 0., a);
>>   	igt_paint_color_alpha(cr, 0, h / 2,     w / 2, h / 2, 0., 0., 1., a);
>> @@ -197,7 +198,8 @@ static void prepare_crtc(data_t *data, igt_output_t *output, enum pipe pipe)
>>   			      &data->argb_fb_0);
>>   
>>   		cr = igt_get_cairo_ctx(data->gfx_fd, &data->argb_fb_0);
>> -		igt_paint_color_alpha(cr, 0, 0, w, h, 0., 0., 0., 1.0);
>> +		cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
>> +		igt_paint_color_alpha(cr, 0, 0, w, h, 0., 0., 0., 0.0);
>>   		igt_put_cairo_ctx(data->gfx_fd, &data->argb_fb_0, cr);
>>   
>>   		igt_create_fb(data->gfx_fd, w, h,
>> -- 
>> 2.17.1
>>
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>