dumping SkSVGCanvas to PNG and XML-string

[kat...@gmail.com]

Hi,

I have the following piece of code and want to do two things:

1- how can I get the relative xml string from SkSVGCanvas ?

2- how can I dump SkSVGCanvas to a PNG buffer? 

Thanks

Hoss

 SkDynamicMemoryWStream svgStream;

 std::unique_ptr<SkXMLWriter> xmlWriter(
 new SkXMLStreamWriter(&svgStream));
 SkRect bounds = SkRect::MakeIWH(2000, 2000);
 std::unique_ptr<SkCanvas> svgCanvas = SkSVGCanvas::Make(bounds, &svgStream);
 

 SkPaint strokePaint;
 strokePaint.setStyle(SkPaint::kStroke_Style);
 strokePaint.setColor(SK_ColorBLACK);
 strokePaint.setAntiAlias(true);
 strokePaint.setStrokeWidth(5);
 static SkScalar x,y, x2,y2;
 static double angle = M_PI/6;
 

 for (int i = 0; i < 10000; i++)
 {
 x2+=5;
 y = 400+sin(angle/2)*300;
 angle += M_PI/6;
 y2 = 400+sin(angle/2)*300;
 svgCanvas->drawLine(x,y,x2,y2,strokePaint);
 x = x2;
 }

 svgCanvas->save();

[Yesenia Jenkins]

[Florin Malita]

On Fri, May 3, 2019 at 11:05 AM <kat...@gmail.com> wrote:

Hi,

I have the following piece of code and want to do two things:

1- how can I get the relative xml string from SkSVGCanvas ?

The XML output is directed to the backing stream - svgStream.  You can grab it as an SkData using svgStream.detachAsData() and go from there.

(IIRC you need to destroy svgCanvas first, to force it to flush)

 

2- how can I dump SkSVGCanvas to a PNG buffer? 

Do you want the result of rasterizing SVG (Skia -> SVG -> raster), or the result of rasterizing Skia draw commands (Skia -> raster)?

Neither is directly available from SkSVGCanvas, but there are ways to generate - depending on which one you need.

 

Thanks

Hoss

 SkDynamicMemoryWStream svgStream;

 std::unique_ptr<SkXMLWriter> xmlWriter(
 new SkXMLStreamWriter(&svgStream));
 SkRect bounds = SkRect::MakeIWH(2000, 2000);
 std::unique_ptr<SkCanvas> svgCanvas = SkSVGCanvas::Make(bounds, &svgStream);
 

 SkPaint strokePaint;
 strokePaint.setStyle(SkPaint::kStroke_Style);
 strokePaint.setColor(SK_ColorBLACK);
 strokePaint.setAntiAlias(true);
 strokePaint.setStrokeWidth(5);
 static SkScalar x,y, x2,y2;
 static double angle = M_PI/6;
 

 for (int i = 0; i < 10000; i++)
 {
 x2+=5;
 y = 400+sin(angle/2)*300;
 angle += M_PI/6;
 y2 = 400+sin(angle/2)*300;
 svgCanvas->drawLine(x,y,x2,y2,strokePaint);
 x = x2;
 }

 svgCanvas->save();

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[kat...@gmail.com]

Thanks for the reply.

- XML output:

I tried the below code but still cant see a thing...

sk_sp<SkData> data = svgStream.detachAsData();
fwrite(data->data(), data->size(), 1, stdout);

- PNG output:

Do you want the result of rasterizing SVG (Skia -> SVG -> raster), or the result of rasterizing Skia draw commands (Skia -> raster)?

ideally, the latter one. but it'd be great if i can see both.

there is also a function in skiaserve called Request::writeCanvasToPng but when i pass my canvas to it, i am hitting the assert within it.. 

SkAssertResult(canvas->readPixels(bmp, 0, 0)); 

but let me not confuse you, i still want the PNG in a buffer as I would to embed it in my application which then in turn sends it to a browser. 

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[Florin Malita]

From: <kat...@gmail.com>
Date: Mon, May 6, 2019 at 5:53 AM
To: skia-discuss

Thanks for the reply.

- XML output:

I tried the below code but still cant see a thing...

sk_sp<SkData> data = svgStream.detachAsData();
fwrite(data->data(), data->size(), 1, stdout);

Not sure why.  This works as expected for me at HEAD:

    SkDynamicMemoryWStream svgStream;

    SkRect bounds = SkRect::MakeIWH(2000, 2000);

    auto svgCanvas = SkSVGCanvas::Make(bounds, &svgStream);

    SkPaint strokePaint;

    strokePaint.setStyle(SkPaint::kStroke_Style);

    strokePaint.setColor(SK_ColorBLACK);

    strokePaint.setAntiAlias(true);

    strokePaint.setStrokeWidth(5);

    static SkScalar x,y, x2,y2;

    static double angle = M_PI/6;

    for (int i = 0; i < 10000; i++)

    {

     x2+=5;

     y = 400+sin(angle/2)*300;

     angle += M_PI/6;

     y2 = 400+sin(angle/2)*300;

     svgCanvas->drawLine(x,y,x2,y2,strokePaint);

     x = x2;

    }

    svgCanvas = nullptr; // force-flush to stream

    auto data = svgStream.detachAsData();

    fwrite(data->data(), data->size(), 1, stdout);

Output:

<?xml version="1.0" encoding="utf-8" ?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="2000" height="2000">
<path fill="none" stroke="rgb(0,0,0)" stroke-width="5" stroke-miterlimit="4" d="M0 477.646L5 550"/>
<path fill="none" stroke="rgb(0,0,0)" stroke-width="5" stroke-miterlimit="4" d="M5 550L10 612.132"/>
        ...

 

- PNG output:

Do you want the result of rasterizing SVG (Skia -> SVG -> raster), or the result of rasterizing Skia draw commands (Skia -> raster)?

ideally, the latter one. but it'd be great if i can see both.

there is also a function in skiaserve called Request::writeCanvasToPng but when i pass my canvas to it, i am hitting the assert within it.. 

SkAssertResult(canvas->readPixels(bmp, 0, 0));

Right, SkSVGCanvas is not backed by pixels.

You have to explicitly draw the same content to a rasterizing canvas, then grab the result from there.  You can use an SkNWayCanvas to draw to both targets at the same time (untested):

...

auto rasterSurface = SkSurface::MakeRasterN32Premul(bounds.width(), bounds.height());

auto dispatchCanvas = sk_make_sp<SkNWayCanvas>();

dispatchCanvas->addCanvas(rasterSurface->getCanvas());

dispatchCanvas->addCanvas(svgCanvas.get());

// now draw to dispatchCanvas instead of svgCanvas

dispatchCanvas->lineTo(...);

...

// grab the XML output as before

...

// grab the raster result

auto rasterImage = rasterSurface->makeImageSnapshot();

auto pngData = rasterImage->encodeToData();

 

If you want to rasterize the SVG output, you can use SkSVGDOM (under experimental/svg) and render to a raster surface same as above, or an external SVG renderer (since SkSVGDOM only supports a limited set of SVG features).

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[Hoss Ajallooiean]

Many thanks.

I have updated my HEAD and now its working.