Fwd: MakeFromStream is not available in Canvaskit

[Steven Whelan]

Hi, 

In C++,I am trying to read a .skp file as SKPicture as below

const char* skpFilePath = "layer_0.skp";

SkFILEStream stream(skpFilePath);

sk_sp<SkPicture> skPicture =SkPicture::MakeFromStream(&stream);

canvas->drawPicture(skPicture.get());

This C++ code works fine. I want to do this in browser. I believe skia cannot run in browser without CanvasKit js binding.

But I cannot find any of these methods in Canvaskit.

I don't think there is any way to run a native C++ command in browser other than using JS bindings.

[John Stiles]

I believe you are looking for "MakePicture":

https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/modules/canvaskit/npm_build/types/index.d.ts;l=414;drc=98601d1c3ff4b6c8460e7b4422b89e8ffbd72693

CanvasKit is not a perfect 1:1 mirror of Skia. It doesn't have the concept of files, for instance, so SkFILEStream is out (in fact, all the stream methods are unsupported). If there is something critical missing that you need, it is probably possible to add a binding, and you can submit a patch in Gerrit to add it to mainline Skia, but make sure to look for alternatives first.

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[Steven Whelan]

Thanks John

I am now trying to load this .skp file in javascript and then trying to use MakePicture command to get SKPicture.

However I am getting the picture as null.

The corresponding C++ code works fine on the same .skp file. Also, I have verified in skia debugger  that the file is not corrupt.

if (file) {
console.log('File is not null');
const reader = new FileReader();
reader.onload = function(e) {
const buffer = e.target.result;
// Initialize CanvasKit and use the buffer as before...
CanvasKitInit({
locateFile: (file) => `https://unpkg.com/canvask...@0.39.1/bin/${file}`
}).then((CanvasKit) => {
// Create an SkPicture object from the .skp file
console.log('buffer:', buffer);
const picture = CanvasKit.MakePicture(buffer);

The buffer is not null, but the picture is.

What could I be doing wrong?

[kjlu...@google.com]

We do have tests for loading in skps from bytes: https://github.com/google/skia/blob/dde1f5dba18343252c185dee776e653bf6049b1b/modules/canvaskit/tests/core_test.js#L894-L900

Perhaps see if you and us are doing anything different; maybe that buffer is not quite the right type?

[Steven Whelan]

Thank you for your response.

I am able to render the .skp file generated in the test - which is also available for download here - https://fiddle.skia.org/c/cbb8dee39e9f1576cd97c2d504db8eee

But I am not able to render the .skp file that is generated by SKIA Debugger. Could it be because of the large size?

Thanks

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[Steven Whelan]

I generated the .skp for google.com through SKIA Debugger which I am trying to load via javascript

[Steven Whelan]

Thank you for your response.

MakePicture is not null for  the .skp file generated in the test - which is also available for download here - https://fiddle.skia.org/c/cbb8dee39e9f1576cd97c2d504db8eee

But when I load .skp file layer_0.skp generated from Chromium for google.com using the steps mentioned here - https://skia.org/docs/user/tips/  then MakePicture returns null.

Could size be a reason?

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[John Stiles]

We won't be able to debug this for you, unfortunately. Please use a debugger and step through to see where it is failing. 

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[Steven]

Hi I am sorry to be asking this question again.

I  am using the same MakePicture Code that was pointed out to me earlier - https://github.com/google/skia/blob/dde1f5dba18343252c185dee776e653bf6049b1b/modules/canvaskit/tests/core_test.js#L894-L900

However, MakePicture is returning null for all .SKP files apart from the one used in the above example.

I have tested almost all .SKPs from https://fiddle.skia.org/named/ but none of them is working.

On debugging canvaskit.js , I found out that  MakePicture internally calls this method

a._MakePicture  which further calls y = p ? b[0].fromWireType(N) : void 0;

 From here var d = this.Tf(a);  and then finally this.wf(a)   which returns 0 even if a is not 0. This makes the whole result null.

I don't know why one .SKP is working and no other Fiddle.org SKPs are working.

Could you please help me on what could be the issue or how I can debug it better?