Speedup drawing of reversed elements

[M-Mommsen]

InvertDraw calls are very slow, so this is an attempt to reduce them as much as possible by drawing only one inverted canvas for all reversed elements and even this one only if needed.
In my tests with a GLS label, the calculation time went from ~12s to 1s !

[YipingRuan]

Very cool.

[M-Mommsen]

In theory there is one condition where the result would be "wrong". That would be reversing an already reversed pixel. But the calculation time of over 10s is simply not acceptable. Maybe there is a faster function available for combining the bitmaps.

[YipingRuan]

Is it possible to provide your sample label for my testing, if no privacy issue?

At the moment please leave this as draft.

[tinohager]

The result is no longer correct with the changes.

Correct

Incorrect

[tinohager]

I have already thought about this topic. But I haven't got around to optimizing the logic yet. The time consuming part is the verification of each pixel. The bigger the label is, the longer it takes. A sensible solution would therefore be to determine where in the last step was drawn and to match only this area I think with this solution this step could be significantly accelerated.

[M-Mommsen]

Is it possible to provide your sample label for my testing, if no privacy issue?

At the moment please leave this as draft.

https://pastebin.com/F4djyBEX

I did all this for EPL once. Back then I decided to just paint with reversed colors. I directly drew to a windows form and speed was essential (and I needed texts to be selectable, highlightable and to support text copy). There was no noticable delay, and now we need to switch from epl to zpl. With a 10 second delay nobody would want to use that app anymore. So maybe a 'draft' or 'preview' rendering mode could help ?

Btw. my final step will now be adding datamatrix support. But I guess I will open a separate issue for that. Those 2D barcodes are also part of every GLS label - and probably any other real life shipping label.

[M-Mommsen]

What about using XOR SKBlendMode for reversed drawing in the first place ?
I did not attempt this, because it looks like a major change, and I don't programm that much C# , but at first glance, setting
skPaint.BlendMode = SKBlendMode.Xor;
should work.
Other possibility would be to use bitblit to combine the canvas'.

[tinohager]

What about using XOR SKBlendMode for reversed drawing in the first place ?
I did not attempt this, because it looks like a major change, and I don't programm that much C# , but at first glance, setting
skPaint.BlendMode = SKBlendMode.Xor;
should work.
Other possibility would be to use bitblit to combine the canvas'.

I'll check that I haven't had time to deal with this module yet.

[M-Mommsen]

The result is no longer correct with the changes.

Correct

Incorrect

btw. I think the images are switched, the correct one is the one that shows double inversions.

[tinohager]

@M-Mommsen Can you print our test label on an original Zebra Printer?

[tinohager]

@M-Mommsen i have create a test script with the SKBlendMode.Xor

The blend mode of SKBlendMode.Xor (exclusive OR) causes nothing to appear where the two areas overlap

using var skBitmap = new SKBitmap(100, 40);
using var skCanvas = new SKCanvas(skBitmap);
skCanvas.Clear(SKColors.White);

using var skPaint = new SKPaint();
skPaint.Style = SKPaintStyle.Fill;
skPaint.BlendMode = SKBlendMode.Xor;

skPaint.Color = SKColors.White;
skCanvas.DrawRect(10, 10, 20, 20, skPaint);
skPaint.Color = SKColors.White;
skCanvas.DrawRect(20, 10, 20, 20, skPaint);
skPaint.Color = SKColors.White;
skCanvas.DrawRect(30, 10, 20, 20, skPaint);

using var data = skBitmap.Encode(SKEncodedImageFormat.Png, 80);
using var fileStream = new FileStream("test.png", FileMode.Create);
data.SaveTo(fileStream);
fileStream.Flush();

But white to white should be black

^XA

^FO10,10
^GB20,20,10,W,0^FS

^FR
^FO20,10
^GB20,20,10,W,0^FS

^FR
^FO30,10
^GB20,20,10,W,0^FS

^XZ

[M-Mommsen]

The blend mode of SKBlendMode.Xor (exclusive OR) causes nothing to appear where the two areas overlap

That's great!

But white to white should be black

Why ? White = nothing is painted or reversed - so white to white should stay white! Only black and white (or white and black) become black!

Could you try:
^XA
^PR1
^FO100,100
^GB70,70,70,,3^FS
^FO200,100
^GB70,70,70,,3^FS
^FO300,100
^GB70,70,70,,3^FS
^FO400,100
^GB70,70,70,,3^FS
^FO107,110^CF0,70,93
^FR^FDREVERSE^FS
^XZ

This should result in:

One other doc says:
^FR
Configures the current field to reverse the background color, drawing black over white and white over black. This is also known as XOR mode drawing.

[M-Mommsen]

@M-Mommsen Can you print our test label on an original Zebra Printer?

I don't know where the file is located :-( ...
But you could also just use http://labelary.com/viewer.html

[tinohager]

^XA

^FO10,10
^GB20,20,10,W,0^FS

^FR
^FO20,10
^GB20,20,10,W,0^FS

^FR
^FO30,10
^GB20,20,10,W,0^FS

^XZ

Just tested on an original Zebra printer. White on white results in black.

[M-Mommsen]

Just tested on an original Zebra printer. White on white results in black.

Hmm - documentation is different. So is it a printer quirk ? We could simulate this behaviour by ignoring the W parameter when printing reversed.

^XA

^FO10,10
^GB20,20,10,W,0^FS

^FR
^FO20,10
^GB20,20,10,B,0^FS

^FR
^FO30,10
^GB20,20,10,B,0^FS

^XZ

Yes - just tested it with the same result! So the zebra is simply ignoring the color in reverse mode!

[YipingRuan]

@M-Mommsen
Try the new master?
Will not be in NuGet until @tinohager increases the package version.

[M-Mommsen]

@M-Mommsen
Try the new master?

The rendering now takes ~0.6s, which is still not great, but so much better than the 10s plus before!