B4J Question Draw on canvas left to right OK, no left to Right

hibrid0 · Jan 3, 2019

Hi I'm learing how to use canvas and I like it.
But my knowledge about geometry is really bad, I need to read it again.
I try to draw rectangles and work so so, that's because I can draw the rectable if I paint from the left to the right, but I paint the right to the left not show the rectangle. I show my bad code.

B4X:

        Rectangulo.Top=posY_at_click
        Rectangulo.Left=posX_at_click
        Rectangulo.Bottom = y
        Rectangulo.Right= X
        canvas_temp.DrawRect(Rectangulo, xui.Color_Black, False, 2)

I try to draw an arrow with B4xpath and .Lineto and I cant at the moment, then I try with draw a bitmap with an arrow inside and goes crazy in some rotations.

B4X:

        Rectangulo.Top=posY_at_click
        Rectangulo.Left=posX_at_click
        Rectangulo.Bottom = y
        Rectangulo.Right= X
        angulo = ATan2D(Y-posY_at_click, x-posX_at_click)
        canvas_temp.DrawLine(posX_at_click, posY_at_click, X, Y, xui.Color_Black, 2)
        canvas_temp.DrawBitmapRotated(fx.LoadImageSample(File.DirAssets, "flecha1.png", 80dip, 80dip),Rectangulo, angulo)

Arrow Video:
Rectangle:

Daestrum · Jan 3, 2019

Your code assumes X is always greater than posX_at_click. drawing right to left this is not true. (same for Y too)

hibrid0 · Jan 4, 2019

Daestrum said:
Your code assumes X is always greater than posX_at_click. drawing right to left this is not true. (same for Y too)

B4X:

        If posY_inicio < y  Then
            Rectangulo.Top=posY_inicio
            Rectangulo.Left=posX_inicio
            Rectangulo.Bottom=y
            Rectangulo.Right=x
        else if posY_inicio > y Then
            Rectangulo.Top=y
            Rectangulo.Left=posX_inicio
            Rectangulo.Bottom=posY_inicio
            Rectangulo.Right=x
        else if posX_inicio < x Then
'            Rectangulo.Top = posY_inicio
'            Rectangulo.Left = x
'            Rectangulo.Bottom = y
'            Rectangulo.Right = posX_inicio
        Else if posX_inicio > x Then
            Rectangulo.Top = y
            Rectangulo.Left = x
            Rectangulo.Bottom = posY_inicio
            Rectangulo.Right = posX_inicio
        End If
canvas_temp.DrawRect(Rectangulo, xui.Color_Black, False, 2)

Now work from down to top, but not left to right, on the best case show a line from the left to the right.

B4J Question Draw on canvas left to right OK, no left to Right

hibrid0

Active Member

Daestrum

Expert

hibrid0

Active Member

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B4J Question Draw on canvas left to right OK, no left to Right

hibrid0

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Daestrum

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hibrid0

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