[OpenJDK 2D-Dev]  Review request for 8023794: [macosx] LCD Rendering hints seems not working without FRACTIONALMETRICS=ON
campbell at plausible.coop
Wed Mar 25 17:24:33 UTC 2015
That's a good find re: pow(). In the comment at lines 277-283 I
mentioned that there was only a scalar variant of pow(). I wonder if
that was a limitation in some early version of GLSL I was using or
perhaps some driver bug/restriction. According to all the docs I can
find the vector variants have been there all along:
So now I'm wondering if the slowness was actually due to me trying 3
scalar pow() calls versus one vector pow() call.
Oh, aha! I think this explains part of it:
269 * This is the GLSL fragment shader source code for rendering
270 * text. Do not be frightened; it is much easier to understand
271 * equivalent ASM-like fragment program!
Looks like I wrote the original version of this shader using the
GL_ARB_fragment_program language, which indeed only had a scalar POW
instruction (see section 188.8.131.52):
And then I'm guessing that when I rewrote it in more modern GLSL, I
didn't notice that pow() supported vectors. Sigh. That 3D texture LUT
was a lot of work for a whole lot of nothing.
In any case, you might want to rewrite the comment at lines 277-283 to
suit the new code. Same goes for the comment at line 315:
// gamma adjust the dest color using the invgamma LUT
Also, I noticed that the restrictions in
OGLContext_IsLCDShaderSupportAvailable() could be loosened since you
only need 2 texture units now. Just in the extremely unlikely case that
anyone's running this stuff on ancient hardware :)
Andrew Brygin wrote:
> Hello Phil,
> could you please take a look to updated version of the fix?
> * OGLTextRenderer.c
> It was discovered, that in some cases lcd glyphs had visible 'dark
> border' around.
> This border appeared due to the gamma correction in lcd shader, which
> uses lookup
> on 3D texture instead of using 'pow' routine. The texture is populated
> with significant
> granularity (16 points per edge), what is a root cause of rough
> interpolation of color values.
> Suggested change is to eliminate the interpolation and use 'pow' routine
> It gives more accurate color values, and does not introduce significant
> performance hit
> (see benchmark summary below).
> However, this part of the fix affects not only macosx, but any platform
> where OGL text
> shader can be used, so it probably worth to split into a separate fix.
> Number of tests: 4
> Overall average: 42.68027553311743
> Best spread: 3.49% variance
> Worst spread: 29.59% variance
> (Basis for results comparison)
> Number of tests: 4
> Overall average: 42.468941501367084
> Best spread: 2.51% variance
> Worst spread: 29.44% variance
> Comparison to basis:
> Best result: 103.28% of basis
> Worst result: 97.36% of basis
> Number of wins: 1
> Number of ties: 2
> Number of losses: 1
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