<AWT Dev>  Review Request: JDK-8159142 : Visible artifacts in sun/java2d/SunGraphics2D/DrawImageBilinear.java
pankaj.b.bansal at oracle.com
Fri Nov 3 09:41:07 UTC 2017
XRSurfaceData, GLXSurfaceData: On linux, only integer scale is supported. If we give non-integer, the the uiScale is truncated to integer and used. So the ceil or round does not matter. In both XRSurfaceData and GLXSurfaceData, ceil function or direct multiplication is used arbitrarily at different places. So, we can make changes for making things more consistent, but it is not necessary as of now.
PS: There are artifacts in same test case on Linux and there is a separate bug https://bugs.openjdk.java.net/browse/JDK-8189957. But these don't seem to be result of this precision error. I will look into this bug later.
WGLSurfaceData: In openGL, ceil function is used in WGLSurfaceData, so it will create WGLOffScreenSurfaceData and in turn create native resource. Then in DrawImage class, the clipRound is used, and these sizes are sent to native size. Then in OGLBlitTextureToSurface function inside OGLBlitLoops file, the texture coordinates are calculated by dividing the sizes sent from Java side by the native resource size. So the texture coordinates are wrong. For instance, in DrawImageBilinear, the size is 5x5 and uiScale is 2.5, so the native resource is of size, 13x13. But the dimensions sent to native are 12x12, so the textures are (0,0) and (12/13, 12/13). So artifacts in final image.
D3DSurfaceData: In D3D, everything is similar to OpenGL, but in D3DBlitTextureToSurface function inside D3DBlitLoops file, the calculated texture coordinates are sent to D3DDrawTextureWithHint and then data is copied from texture to surface. Here if the native resource size and dimensions sent from Java are not same, the data is copied in parts. This is somehow handling the wrong texture coordinates. So this test does not produce any artifacts in D3D pipeline. But it can in some other case. So this needs to be fixed.
GDIWindowSurfacedata: Here the volatile image creates a BufImageSurfaceData as backing resource using the ceil function and while copying from BugImageSurfaceData to a GDIWindowSurface, the Java_sun_java2d_loops_TransformHelper_Transform in native side is able to handle the difference in sizes. So the artifacts are not visible. But I think this should be fixed. So should make changes to getBackupImage function in SunVolatileImage to use clipRound instead of ceil.
BufImageSurfaceData : It uses the image raster size to create the native resource. The raster size is already scaled according to the uiScale. So no need to change this.
So in a nutshell,
I feel we may not change the code in XRSurfaceData, GLXSurfaceData as linux only support integer scaling. We can do it later if required.
We should change code for D3DSurfaceData, GDIWindowSurfacedata and WGLSurfacedata as it may cause artifacts. I have updated the webrev for the same. Please review.
From: Sergey Bylokhov
Sent: Wednesday, November 1, 2017 11:46 PM
To: Pankaj Bansal; awt-dev at openjdk.java.net
Subject: Re: <AWT Dev>  Review Request: JDK-8159142 : Visible artifacts in sun/java2d/SunGraphics2D/DrawImageBilinear.java
D3DSurfaceData, XRSurfaceData and probably other SurfaceData use simple multiplication or ceil(). Should we update them also? and the test to catch the errors there as well.
On 30/10/2017 03:39, Pankaj Bansal wrote:
> Hi All,
> Please review the fix for JDK 10.
> The test runs with D3D and OpenGL both. The issue is with the OpenGL
> run as there aee some visual artifacts in image when the HiDPI scale
> is set to non-integer value like 2.5.
> The issue is due to precision error. In WGLSurfaceData.java, the width
> and height is calculated by multiplying the width and height with scale.
> But the ceil function was being used instead of round. It should be
> using round as at most of the places, the round function is being used.
> Also changed the test to run at uiScale of 2.5 to catch any further errors.
> Pankaj Bansal
Best regards, Sergey.
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