False negative when trying to blend to undefined framebuffer?

[haasn]

I had a bug in my application in which I was trying to blend onto a renderpass attachment that was specified as initialLayout = VK_IMAGE_LAYOUT_UNDEFINED, loadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE, which causes the framebuffer contents to be undefined at the time of blending.

It's definitely possible that the layers could have caught the combination of this + blending enabled, either as a hard error (undefined behavior?) or as a best practices check. Although in theory it's possible that the undefined behaviour is hidden if the specifics of the blending end up with the target being completely discarded, in cases where this can be guaranteed the user could definitely be disabling blending.

Side note, it might be possible to generalize this sort of "detect undefined image contents" by adding some sort of verification feature that explicitly initializes image regions by a static "test" pattern whenever they effectively become undefined (e.g. by transitioning out of VK_IMAGE_LAYOUT_UNDEFINED).

[mark-lunarg]

Added to the best-practices tracking issue #24, will track there. Thanks!