[OpenJDK 2D-Dev]  RFR JDK-8176795: Wrong color drawn when painting translucent colors on volatile images using XRender.
philip.race at oracle.com
Mon Dec 11 18:45:27 UTC 2017
The explanation sounds reasonable, although I'd like to give Clemens a
chance to review this.
On 12/07/2017 07:16 AM, Jayathirth D V wrote:
> Hello All,
> Please review the following fix in JDK10 :
> Bug : https://bugs.openjdk.java.net/browse/JDK-8176795
> Webrev : http://cr.openjdk.java.net/~jdv/8176795/webrev.00/
> Issue : When we draw translucent color over an opaque color in Unix
> from JDK 8 we get different color after composition compared to any
> other platform.
> Root cause : From JDK 8, X Rendering extension is enabled in Unix and
> we see this problem only when we use XRender in Unix if we use GLX or
> X11 we don’t see any issue. Also X Rendering extension expects
> pre-multiplied alpha color values, so we need to convert the
> non-premultiplied alpha color values to pre-multiplied alpha color
> values before give pixel value to XRender for drawing. The main
> problem is we do this operation of conversion twice:
> 1)When we call Graphics2D.setColor() it uses ArgbPre PixelConverter
> based on SurfaceData(here it is XRenderPixMap ArgbPre surface) and
> converts the color to pre-multiplied values.
> 2)When we call Graphics2D.fillRect() internally before we compose the
> destination(opaque color) and source(translucent color) we prepare
> source render rectangle for X Render extension. Here again we convert
> the already converted color values to premultiplied values.
> Solution : There is no need for us to do non-pre to pre color
> conversion again at XRender level so it should be removed. Also this
> logic of non-pre to pre color conversion at XRender was only used when
> source is Solid color and not Texture/Gradient. So I have completely
> removed this logic itself as it not needed anywhere else.
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