Canvas questions
lazarus / 39-Graphics

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Blestan · 2013-04-02 20:27

hi! i have 2 questions about canvas
1/ how to get update rect on overiding paint method in multiplatform
way...
2/ how to set viewport org to offset all draw operations on the
canvas...
thanks

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Blaazen · 2013-04-02 21:22

I don't understand the questions very well.

To 1) I think you are looking for InvalidateRect, it means that only
part of component's canvas is repainted. It works well on Qt and GTk2.

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Blestan · 2013-04-03 05:37

hummmm....
1. updaterect structure must me available during
paint. invalidaterect just add another rect to
list of invalid regions...
2. setviewport allows to set
an origin to all drawing operations,  so you can for
example draw at negative coordinates and still view
the drawing on the control.

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User137 · 2013-04-03 09:36

There is no origin property on TCanvas. You can make your own TPoint
variable for origin, and decrease it from every coordinate you use for
drawing.

Example, origin:=point(100, 100).
Draw picture to (120-origin.x, 120-origin.y)
So now picture is drawn to (20, 20), relatively to origin.