[Lazarus] Fast drawing to canvas

[Darius Blaszyk]

Despite all the advices, none of the suggestions of drawing on a TPaintBox or creating a TCustomControl actually speed up the painting significantly. Therefore I did some profiling. It appears that loading a 40kb png file (50% HD) from a stream takes about 60msec another 30msec is used to paint the bitmap to screen. It all results in approx. 11fps which is actually pretty poor when you imagine a full HD loop will make the rate drop 2.5fps. 

As I see it now, I will need to lower the access time to the png's from disk. I will do a test with storing only raw pixel data instead. This means that there will be no conversion (or decompression in the case of PNG) when streaming from disk. However, although the minor part of the total loop, I was hoping to improve the painting speed significantly as well. Hopefully someone else has an idea that works.
Is there a way to access even lower level functions from LCL? Like GDI and GTK2 functions to copy the pixel data as fast as possible?

Appreciate the help from everybody so far.

Regards, Darius




On Feb 8, 2012, at 5:12 PM, Sven Barth wrote:

> Am 08.02.2012 16:02, schrieb dhkblaszyk at zeelandnet.nl:
>> I have played with Image.Update, .Invalidate and .Repaint, but none of
>> them seem to work for me. Only when I put Application.ProcessMessages
>> the painted images show on screen. See below for the testloop code. The
>> images are streamed from a file cache. For 24 frames this seems
>> overkill, but running at 24fps the memeory requirements quickly get very
>> large!
>> 
>> Image.Transparent is also set to false btw, which is default. Otherwise
>> the drawing on the canvas is even messed up.
>> 
>> Regards, Darius
>> 
>> procedure TForm1.Button1Click(Sender: TObject);
>> var
>> s: TDateTime;
>> i: Integer;
>> begin
>> s := now;
>> for i := 1 to 24 do
>> begin
>> if filecache_get_from_cache(i, png) then
>> begin
>> Image1.Picture.Bitmap.LoadFromRawImage(png.RawImage, False);
>> Application.ProcessMessages;
>> end;
>> end;
>> 
>> ShowMessage(FloatToStr(24 / ((now - s) * 24 * 3600)))
>> end;
> 
> Here it is clear that you need to use Application.ProcessMessages, because "LoadFromRawImage" will only tell the control that it needs to repaint itself, but does not execute this repainting (this is done in Application.ProcessMessages). In the example you posted in the beginning the call to Application.ProcessMessages is located inside the OnPaint handler of the Image which is - in my opinion - not good. Maybe also the loading of the image inside the OnPaint handler is not good...
> 
> Maybe you should try - like Felipe suggested - something else than TImage. Try for example TPaintBox in combination with the Application.OnIdle event:
> 
> procedure TForm1.ApplicationOnIdle(aSender: TObject; var aDone: Boolean);
> begin
>  LoadNextImageFromCache; // this will load the next image into some private variable of the form (let's call it fImage). [this is based on your filecache_get_from_cache any you'll need to write it of course ;) ]
>  PaintBox1.Invalidate;
>  aDone := False; // important!
> end;
> 
> procedure TForm1.PaintBox1Paint(aSender: TObject);
> begin
>  PaintBox1.Canvas.Draw(fImage); // or however you'll get the content of the fImage onto the canvas of the PaintBox
> end;
> 
> Note: Don't forget to assign your ApplicationOnIdle to Application.OnIdle or use the ApplicationProperties component located in the Additional tab.
> 
> Regards,
> Sven
> 
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