Generate mipmaps for image down-scaling
AbandonedPublic

Authored by romangg on Mon, Sep 2, 10:18 AM.

Details

Reviewers
zzag
Group Reviewers
KWin
Maniphest Tasks
T10481: Improve scaled buffer rendering
Summary

Without generating mipmaps the output of via glViewport down-scaled images
is blurry when not being scaled by an integer value.

Test Plan

Tested on an Intel setup where the image is fine afterwards. On an AMD setup
I have a crash in mesa (experimental mesa ACO branch).

Diff Detail

Repository
R108 KWin
Branch
mipmapScaling
Lint
Lint OK
Unit
No Unit Test Coverage
Build Status
Buildable 15998
Build 16016: arc lint + arc unit
romangg created this revision.Mon, Sep 2, 10:18 AM
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romangg requested review of this revision.Mon, Sep 2, 10:18 AM

Thanks, I was under the impression we needed to enable smooth filtering, but to me the output always looked the same.

plugins/scenes/opengl/scene_opengl.cpp
1383

That's a bit lazy.

Always using GL_LINEAR AFAIK is fine, but always generating mipmaps has a cost.

We should be able to do some sort of

if (windowPixmap->surface()->scale() != output->scale())

We also probably only want to generate mipmaps if the contents have changed.

GLTexture has a dirty() flag which signifes this.

zzag requested changes to this revision.Mon, Sep 2, 2:15 PM
zzag added a subscriber: zzag.

One need to set a mipmapping minimification filter, like GL_LINEAR_MIPMAP_LINEAR, in order to actually use mipmaps.

However, do we actually have to worry about noise level? I don't think so. GL_LINEAR should be more than enough.

plugins/scenes/opengl/scene_opengl.cpp
1495–1497

I don't understand this part. Window contents is rendered and after that mipmaps are generated. I think it should be vice versa.

This revision now requires changes to proceed.Mon, Sep 2, 2:15 PM
romangg added inline comments.Thu, Sep 5, 10:39 AM
plugins/scenes/opengl/scene_opengl.cpp
1383

if (windowPixmap->surface()->scale() != output->scale())

One would need to loop through all surface-entered outputs and check if logical size and mode size don't have a common divisor. I can't say if that would be worth it or if we should create mipmaps just all the time. After all they are generated on the GPU and that very fast.

We also probably only want to generate mipmaps if the contents have changed.

GLTexture has a dirty() flag which signifes this.

This makes sense. But can you explain to me how the dirty() flag actually works? I see that it gets set at some point but I don't see where it gets unset again.

1495–1497

Why do you think it should be vice versa?

Mipmaps are scaled down copies of a texture such that arbitrary down-scaling can be done quickly and without artifacts. That means the original must have been rendered already so it can be duplicated.

Maybe in the end it doesn't make a difference because it's a Gl command on the GPU.

In D23669#524535, @zzag wrote:

One need to set a mipmapping minimification filter, like GL_LINEAR_MIPMAP_LINEAR, in order to actually use mipmaps.

However, do we actually have to worry about noise level? I don't think so. GL_LINEAR should be more than enough.

Hmm, maybe it's indeed enough to just set GL_LINEAR without generating the mipmaps since it looks fine here like that. I have to test on other devices.

zzag added inline comments.Thu, Sep 5, 1:30 PM
plugins/scenes/opengl/scene_opengl.cpp
1495–1497

You need to propagate updates from the base layer up to the maximum layer before mapping the texture. If this code were using mipmaps, you'd render a bit outdated contents.

Let's do a version with with just the gl_linear patch. As that's the only part running in your testing anyway.

Let's do a version with with just the gl_linear patch. As that's the only part running in your testing anyway.

See D23986.

romangg abandoned this revision.Mon, Sep 16, 10:54 AM

Replaced by D23986 with only the filter change but without trying to generate mipmaps. Keeping this in diff separated for reference.