From CrossOver's Programs menu, select Run Command
In the Run Command dialog, select the bottle containing Dota 2
For the command, type regedit
In the Registry Editor, navigate to the key
If the Direct3D folder doesn't exist you can right-click on the Wine folder and pick New>Key. Then name the new key Direct3D.
In the new Direct3D folder if there isn't a key named useGLSL already you can create one by right-clicking, choose New>String Value, and name the new string useGLSL. Then double-click the key to set the value. The value has to be disabled.
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