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I would like to have my material on the object.

Then I want to paint an alpha mask which will be an emission texture material on top of my material. Basically, only part of the object which will emit light will be my painted texture on it. How to do that ?

enter image description here

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First of all, you are going to want to UV unwrap your cube by going into edit mode and using something like "Smart UV Project." If you then go into the "UV / Image Editor" panel, you should see your faces outlined. Go ahead and hit the new button next to the +, and leave the color as black. Click OK and select paint mode from the drop down bar next to the button with a picture of a pin on it. You can now drag while clicking to paint over your texture. When you are done, select "Image > Save as Image" and name and save your texture. If you don't, the texture will be gone when you reopen the blend file. Your texture should look something like this: enter image description here

Now, go back into your "Node Editor" panel, and add a new emission shader, mix shader, and Image Texture. Connect the your base, non-glowing material to the top "shader" input of the mix shader, the emission shader to the bottom "shader" input, and your Image Texture "Color" to the "Fac" input. Finally, in the Image Texture node, select the texture you drew on earlier. What this does is, in the white areas of your texture, the emission is able to show through, whereas the black areas let the base shader show through. Here's a picture of how it should all have come together: enter image description here

In the end, your result should look something like this: enter image description here

Have fun Blendering! Cheers, Graves Broderick

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  • $\begingroup$ Don't mention it! One last thing I forgot to mention, make sure after you paint your texture to select "Image > Save as Image" inside of the "UV / Image Editor" panel. If you don't the texture will be gone when you reopen the file. $\endgroup$ – Zacocast Jun 21 '17 at 6:53
  • $\begingroup$ Ok, thanks. When in paint mode, what is the difference between blend input: mix, add ...? $\endgroup$ – Wildfire Jun 21 '17 at 8:51
  • $\begingroup$ Yes, I didn't save the texture and it's lost when you open it. $\endgroup$ – Wildfire Jun 21 '17 at 8:59
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    $\begingroup$ I'm sorry I didn't tell you it would be gone sooner, you'll have to redo your texture. I wasn't quite sure if I was remembering how it worked correctly when I typed that. Here's a list of the different blend modes you were wondering about. Basically "mix" lays your new color over the top of the color underneath, and "add" actually mixes two colors together (like red and blue making purple). $\endgroup$ – Zacocast Jun 21 '17 at 17:06

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