Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 418.91
Broken: version: 2.80 (sub 64), branch: blender2.7, commit date: 2019-05-14 00:25, hash: rBa5b5bd2c24e0
Worked: 2.80, commit date: 2019-05-11 18:20, hash ebc44aae9897
Short description of error
Current builds of Blender 2.80 seem to be discarding colour information in textures under specific conditions. Any texture you use in a material node tree with an alpha channel and "Use Alpha" turned on displays incorrectly: any pixels that are black on the alpha channel are also black on the red, green, and blue channels . This did not happen with earlier builds and, weirdly, affected images display correctly when viewed in the image editor.
This is leading to the following side effects:
- Opaque parts of alpha transparent textures now have soft black lines around their edges (see included screenshots) and appear more aliased and sharp than they should
- Channel packing -- a technique popular in video game development where several greyscale masks are placed in the red, green, blue, and alpha channels of a texture to save memory, "packing" them into one image that can then be split up and used with a "Separate RGB" node -- now no longer works correctly on an image with an alpha channel since the masks in the red, green, and blue channels are "blacked out"
Exact steps for others to reproduce the error
Drag and drop any texture with an alpha channel (PNG or TGA) into a material node tree. Do not disable "Use Alpha" for the texture. Hook up the Color output to Base Colour. Observe that all pixels where the alpha channel is black are now black in the red, green, and blue channels as well. If necessary, to examine each channel individually, place and connect up a "Separate RGB" converter node. Note this issue persists regardless of whether you're using Eevee or the Cycles render engine.
To help reproduce the bug, I've attached a Targa file below which is a colour gradient with the words "This is a test" written on the alpha channel. This serves as an ideal example of an image that has colour data in the 100% transparent pixels that you can view in Blender's image editor by isolating the "Color" channel.
Also included are two screenshots of the "black lines around edges" issue: "Before.png" is how it looked prior to the bug, "After.png" is how it looks now. Note the considerably more jagged edges to the letters.