Pass device pixel scale via picture render task data.

[gw3583]

As a follow up, we will be able to include a per-picture
local scaling factor. This can be used for drawing pictures
in local space at a specific scale factor.

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This change is 

[gw3583]

r? @kvark

Pending try:
https://treeherder.mozilla.org/#/jobs?repo=try&revision=8b3ba71cedc7c3af0efcaf1e4879e3c339a8e146

[gw3583]

Try run looks good.

[kvark]

my main concern would be testing this. Does Gecko's CI have any bots with non-unit device/pixel ration? if not, would be good to get that build on a few machines and run

Reviewed 15 of 15 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @gw3583)

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webrender/res/snap.glsl, line 18 at r1 (raw file):

    //           the test cases we have in Servo that are failing without it
    //           and seem better than not having this at all.
    snap_rect.size = max(snap_rect.size, vec2(1.0 / device_pixel_scale));

given the number of times we need to divide by it, we should probably provide the reciprocal (as an extra) from CPU side

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webrender/src/device/gl.rs, line 527 at r1 (raw file):

    id: gl::GLuint,
    u_transform: gl::GLint,
    u_device_pixel_ratio: gl::GLint,

🎉

[bors-servo]

☔ The latest upstream changes (presumably #3143) made this pull request unmergeable. Please resolve the merge conflicts.

[gw3583]

Reviewable status: 6 of 15 files reviewed, 2 unresolved discussions (waiting on @kvark and @gw3583)

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webrender/res/snap.glsl, line 18 at r1 (raw file):

Previously, kvark (Dzmitry Malyshau) wrote…

given the number of times we need to divide by it, we should probably provide the reciprocal (as an extra) from CPU side

Filed #3157

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webrender/src/device/gl.rs, line 527 at r1 (raw file):

Previously, kvark (Dzmitry Malyshau) wrote…

🎉

Done.

[gw3583]

Filed #3157 and rebased.

I agree with the testing comment. I did a fair amount of manual testing in wrench with difference ratios, and it seems OK, but I'm not sure how good our CI coverage is. Once I start to leverage this for rasterizing pictures at different scales, we can definitely get some good CI coverage via that.

[kvark]

@bors-servo r+

[bors-servo]

📌 Commit b0d7136 has been approved by kvark

[bors-servo]

⌛ Testing commit b0d7136 with merge 3eff42b...

[bors-servo]

☀️ Test successful - status-appveyor, status-taskcluster
Approved by: kvark
Pushing 3eff42b to master...