Drawing on Canvas is faster than drawing on BGRABitmap

[plashenkov]

Hello!

I'm trying to draw semitransparent image (256 x 256 pixels) on BGRABitmap. And I need to draw it as fast as possible.
I noticed that drawing it on BGRABitmap which I use as internal buffer is critically slower than drawing it directly on Canvas.

Hereby the question: why it is so and is there any way to speed up drawing semitransparent image on canvas?

Here is the image I used:
http://johndyer.name/lab/colorpicker/refresh_web/colorpicker/images/map-hue.png

And the second question: after drawing this image on Canvas, I see slightly visible jaggies.
But when drawing on BGRABitmap, I can see smooth and very fine picture.
Why one image is drawn differently?

Thank you!

[circular]

To draw faster, try using dmLinearBlend instead of dmDrawWithTransparency.

What do you mean by jaggies ? Do you have a screenshot ?

[plashenkov]

Yes, screenshot is attached.

Pictures look almost identical, but if to look very carefully, the jaggies on the left side are visible (usual Canvas-base drawing).

Sure, I use dmLinearBlend for the second picture. It is smooth, but much slower. And I do not know what to do --- I need to repaint picture when changing color in color bar (not presented on screenshot) on mouse move, and it noticeably slows down.

Probably, I can accept the first variant with almost visible jaggies (speed is good in this case), but I do not know how to print the picture with custom master alpha (I will need this too).

Or maybe I do something wrong and there is a way to speed up normal drawing with BGRABitmap?

Thank you very much for your attention to this issue!
Sincerely,
Yury

[plashenkov]

I tried to use CanvasOpacity --- I supposed this propery controls the common master alpha when drawing on Canvas --- but I see no changes in drawing when changing this parameter.

[circular]

Oh it's to draw a color gradient. Well, there are other ways to do that.

- with HSLAToBGRA function to draw each pixel with a PBGRAPixel defined for each ScanLine.
- with FillPolyLinearColor function

CanvasOpacity is only to use LCL functions to draw on the Canvas property, but to define the alpha component (otherwise it is 0 so transparent).

[plashenkov]

Dear circular,

Thank you for your help!