[Webkit-unassigned] [Bug 117705] New: Shader compiler not properly configured for GLES on cairo based ports

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=117705

           Summary: Shader compiler not properly configured for GLES on
                    cairo based ports
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: mario at webkit.org
                CC: mrobinson at webkit.org


At the moment, the ANGLE shader compiler used in GraphicsContext3D for cairo based ports is always speaking GLSL, no matter WebKit is configured to use a GLES2 or an GL backend. This is causing some problems such as that the "precision mediump float;" bit in the fragment shader template used by TextureMapper(see TextureMapperShaderProgram.cpp) gets ignored when compiled by ANGLE, causing problems with some graphics drivers because that will mean that float precision for fragment shaders won't be explicitly specified, which seems to be a requirement for GLES2 (even if some implementations are more relaxed about it).

The solution seems to be as simple as properly configuring the ANGLE compiler when creating the graphics context, to use SH_ESSL_OUTPUT instead of SH_GLSL_OUTPUT when GLES2 is used.

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