[EmulGL] Improve rendering quality on HiDPI Windows10

[jzy3d]

Below chart shows an aliasing improvement required on a chart rendered in Windows10 with HiDPI configuration.

Using CPU based rendering with this aliasing glitch remains a good workaround for the badly scaled native charts with GPU based rendering (which issue can be found here #101)

To reproduce thi aliasing problem

• Run SurfaceDemoEmulGL or ScatterDemoEmulGL from tutorials
• Use Windows10 with HiDPI configuration

[jzy3d]

Interesting comparison of offscreen painting vs onscreen painting quality

[vsonnier]

Maybe it is related with this JFreeChart issue : jfree/jfreechart#170 and a possible fix ?

[jzy3d]

Applying the trick suggested by @vsonnier allows improving the pixel ratio (everything looks thiner), however, it does not deal with the aliasing effect. See work in progress in "hipdpi" branch of jGL. Pull request started to ease review of the changes.

[jzy3d]

Disabling @vsonnier suggestions, then applying the idea of reseting the internal JVM Graphics2D scaling to 1 lead to a too small image but with no aliasing issue.

[jzy3d]

Replacing

Image i = glImage.getScaledInstance(desiredWidth, desiredHeight, Image.SCALE_SMOOTH);
g.drawImage(i, StartX, StartY, o);

by

Image i = glImage;
g.drawImage(glImage, StartX, StartY, desiredWidth, desiredHeight, o);

provides the expected result.

[jzy3d]

Works on MacOS as well, but noticed a rendering performance slightly larger (pixel ratio is 2x on MacOs with Retina, 1.5x on my windows running on Apple hardware with Bootcamp).

• Scatter chart rendering time does not have a perceptible change
• Surface chart rendering time on MacOS goes from ~35ms to ~90ms per frame

[jzy3d]

Can be edited with chart's Quality setting.