Need to calculate viewboxWH (width/height) after loading svg image

[carloBarazzetta]

Hello, at 6 Jan 2025 I need to change my code of Image32SVGFactory from:
vbox := fSvgReader.RootElement.GetViewbox;
to
vbox := fSvgReader.RootElement.viewboxWH;
because GetViewbox was removed from source of Img32.SVG.Reader, but it is also mentioned in a comment line... ;-)

Now the problem is that, after loading an svg file RootElement.viewboxWH is not initialized, so I need to make a change to source code of Img32.SVG.Reader adding a new public method "CalcViewBoxOfRootElement" like this:

procedure TSvgReader.CalcViewBoxOfRootElement;
begin
  fRootElement.viewboxWH.Width := fRootElement.elRectWH.width.GetValue(defaultSvgWidth, 0);
  fRootElement.viewboxWH.height := fRootElement.elRectWH.height.GetValue(defaultSvgHeight, 0);
end;

Or something else that give me a chance to read the viewbox size, after loading file stream or source stream...
Thanks....
Carlo

[AngusJohnson]

Hi Carlo.

I don't understand the problem you're describing, so it'd help if you provided and example.

fRootElement.viewboxWH should be assigned via the Viewbox_Attrib procedure which is called whenever an SVG element's viewbox attribute is encountered.

[jrathlev]

Hello, I have just come across this problem. This issue is relevant if no viewbox is specified in the svg file. Width and Height are then returned as 0. A function CalcViewBoxOfRootElement as described above would solve this problem.

[carloBarazzetta]

In my version of Image32, used by SVGIconImageList I've maintained CalcViewBoxOfRootElement.

Sorry but I forgot to explain to Angus why it is needed with a use case...

[jrathlev]

I had lost this change when I updated Image32. But you should look again in Img32.SVG.Reader. In DrawImage the calculation is executed twice.

[AngusJohnson]

Hi Carlo. Could you please provide a sample SVG file that demonstrates this issue. Cheers.

[AngusJohnson]

Could someone please provide an SVG sample that demonstrates this problem, because I still don't understand what exactly the problem is.

In Img32.SVG.Reader ...

procedure TSvgReader.DrawImage(img: TImage32; scaleToImage: Boolean);
var
  ...
begin
  ...
  with fRootElement do
  begin
    if viewboxWH.IsEmpty then
    begin
      if not elRectWH.IsValid then Exit;  // should never happen
      viewboxWH.Width := elRectWH.width.GetValue(defaultSvgWidth, 0);
      viewboxWH.height := elRectWH.height.GetValue(defaultSvgHeight, 0);
    end;
    // TO GET BEYOND THIS LINE THERE MUST BE A VALID (ie NON-EMPTY) viewboxWH

[carloBarazzetta]

Hi Angus, sorry for the delay. The problem I have is related to the need to implement the "AutoSize" property of my TSVGIconImage component: when I load an SVG image with AutoSize set to True what I get is that the component "adapts" to the default size of the image, so as soon as I load the file I ask the engine to provide me with the default image dimensions: in the case of rendering with Image32, if I load an SVG that does not define width, height and ViewPort (as blur.svg attached), I cannot read the size of the image, so I have moved your code inside TSvgReader.DrawImage:

viewboxWH.Width := elRectWH.width.GetValue(defaultSvgWidth, 0);
viewboxWH.height := elRectWH.height.GetValue(defaultSvgHeight, 0);

into a public method:

procedure TSvgReader.CalcViewBoxOfRootElement;
begin
  fRootElement.viewboxWH.Width := fRootElement.elRectWH.width.GetValue(defaultSvgWidth, 0);
  fRootElement.viewboxWH.height := fRootElement.elRectWH.height.GetValue(defaultSvgHeight, 0);
end;

so the Image32SVGFactory.pas factory can call this method to obtain the X and Y dimensions of the SVG image as the other 2 engines do (2D2 and Skia) after loading the image...

I did this because I couldn't find another way to know the size of the image "blur.svg", but that's probably not the right way either... In fact, if width and height are specified as:
width="12cm" height="5.25cm" as in the arcs.svg attached, I cannot get the size in pixels...

Doing a check with the implementation of the other 2 factories, D2D and Skia4Delphi and comparing the result with the Chrome browser I'm having those results:

Blur.svg

Width and Height in source: not defined
ViewBox in source: not defined

Rendering	Rendered Width	Rendered Height
Chrome	230	120
D2D Factory	230	120
Skia4Delphi	230	120

arcs.svg

width="12cm" height="5.25cm" viewBox="0 0 1200 400"

Rendering	Rendered Width	Rendered Height
Chrome	453	198
D2D Factory	453	198
Skia4Delphi	425	586

I need to find a way to ask the TSvgReader class to return the pixel dimensions of the svg image so that I can implement "autosize" of a TSVGIconImageList like I do for other engines...

[AngusJohnson]

I need to find a way to ask the TSvgReader class to return the pixel dimensions of the svg image

Make sure the TImage32 object is empty (ie zero width and height) before calling its load method.

https://www.angusj.com/image32/Docs/Units/Img32.Fmt.SVG/_Body.htm

• Because vector images scale without losing any image quality, they should be loaded (ie rendered) into TImage32 objects that have been pre-sized. (This avoids the loss of image quality you'll get when scaling raster images.) When loading, the SVG image will scale to best fit the TImage32 object's size, while also preserving its height/width ratio. If you need an image rendered at the SVG image's native size, then make sure the TImage32 object is empty (ie zero width and height) before calling its load method.