canvas.Scale() Bug or bad practice?

[abakoboParticipant]

I’ve encoutered an artifact with canvas.scale
May be we’re not supposed to zoom in but the circle is nice when zoomed so I assume it’s a bug

With the following code you can see that th radius of the circle is not correctly placed when zoomed but is ok when growing the circle.

Monkey

[crayon-5cba8d89b1bf1987216971 inline="true" ] Namespace myapp #Import "<std>" #Import "<mojo>" Using std.. Using mojo.. Class MyWindow Extends Window Field zoom:=1.0 Field radius:=4.2 Field x:=9.3 Field y:=9.2 Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null ) Super.New( title,width,height,flags ) End Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText("Press space to zoom, Enter to grow circle, R to reset",10,10) canvas.Scale(zoom,zoom) canvas.DrawCircle( x,y,radius ) canvas.Color=Color.Black canvas.DrawLine(x,y,x+Cos(0.7)*radius,y+Sin(0.7)*radius) If Keyboard.KeyDown(Key.Space) Then zoom=zoom*1.1 If Keyboard.KeyDown(Key.Enter) Then radius=radius*1.1 If Keyboard.KeyDown(Key.R) zoom=1.0 radius=1.2 Endif Print zoom End End Function Main() New AppInstance New MyWindow App.Run() End

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[crayon-5cba8d89b1bf1987216971 inline="true" ] Namespace myapp   #Import "<std>" #Import "<mojo>"   Using std.. Using mojo..   Class MyWindow Extends Window Field zoom:=1.0 Field radius:=4.2 Field x:=9.3 Field y:=9.2 Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null )   Super.New( title,width,height,flags ) End   Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText("Press space to zoom, Enter to grow circle, R to reset",10,10) canvas.Scale(zoom,zoom)   canvas.DrawCircle( x,y,radius ) canvas.Color=Color.Black canvas.DrawLine(x,y,x+Cos(0.7)*radius,y+Sin(0.7)*radius) If Keyboard.KeyDown(Key.Space) Then zoom=zoom*1.1   If Keyboard.KeyDown(Key.Enter) Then radius=radius*1.1 If Keyboard.KeyDown(Key.R) zoom=1.0 radius=1.2 Endif Print zoom End End   Function Main()   New AppInstance New MyWindow App.Run() End

[/crayon]

[codifiesParticipant]

Monkey

Namespace myapp #Import "<std>" #Import "<mojo>" Using std.. Using mojo.. Class MyWindow Extends Window Field zoom:=.01 Field radius:=400.2 Field x:=9.3 Field y:=9.2 Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null ) Super.New( title,width,height,flags ) End Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText("Press space to zoom, Enter to grow circle, R to reset",10,10) canvas.Scale(zoom,zoom) canvas.DrawCircle( x,y,radius ) canvas.Color=Color.Black canvas.DrawLine(x,y,x+Cos(0.7)*radius,y+Sin(0.7)*radius) If Keyboard.KeyDown(Key.Space) Then zoom=zoom*1.1 If Keyboard.KeyDown(Key.Enter) Then radius=radius*1.1 If Keyboard.KeyDown(Key.R) zoom=.01 radius=400.2 Endif Print zoom End End Function Main() New AppInstance New MyWindow App.Run() End

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Namespace myapp #Import "<std>" #Import "<mojo>" Using std.. Using mojo.. Class MyWindow Extends Window Field zoom:=.01 Field radius:=400.2 Field x:=9.3 Field y:=9.2 Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null ) Super.New( title,width,height,flags ) End Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText("Press space to zoom, Enter to grow circle, R to reset",10,10) canvas.Scale(zoom,zoom)   canvas.DrawCircle( x,y,radius ) canvas.Color=Color.Black canvas.DrawLine(x,y,x+Cos(0.7)*radius,y+Sin(0.7)*radius) If Keyboard.KeyDown(Key.Space) Then zoom=zoom*1.1   If Keyboard.KeyDown(Key.Enter) Then radius=radius*1.1 If Keyboard.KeyDown(Key.R) zoom=.01 radius=400.2 Endif Print zoom End End Function Main() New AppInstance New MyWindow App.Run() End

hows that

there might be a rounding error involved ?

[Mark SiblyKeymaster]

Nice bug! Potential fix pushed to develop branch.

[Author]

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