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I create an offscreen texture with alpha component, samples in the offscreen renderPass is VK_SAMPLE_COUNT_1_BIT. When I use this texture in a VK_SAMPLE_COUNT_4_BIT renderPass, I get black dots pattern where there is an alpha component. I understand why, but I don't know how to solve this problem.

I thought I could use an offscreen renderpass with VK_SAMPLE_COUNT_4_BIT with another VK_SAMPLE_COUNT_1_BIT attachment to resolve into, but my texture would still be VK_SAMPLE_COUNT_1_BIT. So I'm not sure it will solve the black dots issue, and I prefer to seek advice before I get into big changes.

-------- edit 1 --------

The dots appear when I use these VkPipelineMultisampleStateCreateInfo setting:

.alphaToCoverageEnable = VK_TRUE;
.alphaToOneEnable      = VK_TRUE;

If these two setting are set to VK_FALSE, I've got transparent texture but without any gradient, it's transparent or opaque.

Here are my VkPipelineColorBlendAttachmentState setting for both offscreen and texturing renderPass:

.srcColorBlendFactor = VK_BLEND_FACTOR_SRC_ALPHA;
.dstColorBlendFactor = VK_BLEND_FACTOR_ONE_MINUS_DST_ALPHA;
.colorBlendOp = VK_BLEND_OP_ADD;
.alphaBlendOp = VK_BLEND_OP_ADD;

When I look at the offscreen texture with a green "clear color", I can see the gradient of transparency, so I suppose the offscreen renderPass is correctly set.

-------- edit 2 --------

I modified the offscreen renderPass in order to use the same sample count as in the onscreen, or final, renderPass, by hadding a resolve attachment with VK_SAMPLE_COUNT_1_BIT.

I still have dots if I set .alphaToCoverageEnable and .alphaToOneEnable to VK_TRUE. When set to false, the full image is semi-transparent, even the opaques parts.

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  • A render pass doesn't have a sample count; the attachments to a render pass do. And the images you eventually use when you instantiate that render pass must match the sample count you used for the attachments those images get used with. Commented Apr 16, 2020 at 14:53
  • If you could give a bit more details about what you want to achieve, we maybe could give some advice. Do you want to rasterize into multi-sample attachments and resolve the multi-sampled result afterwards into a VK_SAMPLE_COUNT_1_BIT attachment, or is it something else you are trying to do? How do you want to use the texture you are describing with "but my texture would still be VK_SAMPLE_COUNT_1_BIT"? Commented Apr 17, 2020 at 9:52
  • I apply a texture created offscreen on a plan. The texture is half transparent. I want to keep the transparency once apply on the plan. It doesn't really matter if the texture is multi-sample. Commented Apr 17, 2020 at 13:58
  • Nicol > I'll try with a resolve attachment tomorrow. I lost more time turning around the blend settings than testing the more obvious solution. Commented Apr 17, 2020 at 22:16
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