[Webkit-unassigned] [Bug 98962] New: [CSS Shaders] Clamp input colors before blending

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=98962

           Summary: [CSS Shaders] Clamp input colors before blending
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: mvujovic at adobe.com
                CC: dino at apple.com, achicu at adobe.com,
                    luxtella at company100.net
            Blocks: 71392


In CustomFilterValidatedProgram.cpp, we use the following GLSL code to blend the element texture (premultiplied with css_ColorMatrix) and css_MixColor.

mediump vec4 originalColor = texture2D(css_u_texture, css_v_texCoord);
mediump vec4 multipliedColor = css_ColorMatrix * originalColor;
mediump vec3 blendedColor = css_BlendColor(multipliedColor.rgb, css_MixColor.rgb);

The css_BlendColor function and blending in general expects valid color values between [0.0, 1.0]. Thus, we should clamp multipliedColor and css_MixColor to [0.0, 1.0].

If we clamp the input colors to css_BlendColor, css_BlendColor will return a color in the range [0.0, 1.0].

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