70 lines
2.3 KiB
Go
70 lines
2.3 KiB
Go
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package render
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// TrimBox helps with Engine.Copy() to trim a destination box so that it
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// won't overflow with the parent container.
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func TrimBox(src, dst *Rect, p Point, S Rect, thickness int32) {
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// Constrain source width to not bigger than Canvas width.
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if src.W > S.W {
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src.W = S.W
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}
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if src.H > S.H {
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src.H = S.H
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}
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// If the destination width will cause it to overflow the widget
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// box, trim off the right edge of the destination rect.
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//
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// Keep in mind we're dealing with chunks here, and a chunk is
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// a small part of the image. Example:
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// - Canvas is 800x600 (S.W=800 S.H=600)
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// - Chunk wants to render at 790,0 width 100,100 or whatever
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// dst={790, 0, 100, 100}
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// - Chunk box would exceed 800px width (X=790 + W=100 == 890)
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// - Find the delta how much it exceeds as negative (800 - 890 == -90)
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// - Lower the Source and Dest rects by that delta size so they
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// stay proportional and don't scale or anything dumb.
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if dst.X+src.W > p.X+S.W {
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// NOTE: delta is a negative number,
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// so it will subtract from the width.
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delta := (p.X + S.W - thickness) - (dst.W + dst.X)
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src.W += delta
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dst.W += delta
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}
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if dst.Y+src.H > p.Y+S.H {
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// NOTE: delta is a negative number
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delta := (p.Y + S.H - thickness) - (dst.H + dst.Y)
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src.H += delta
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dst.H += delta
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}
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// The same for the top left edge, so the drawings don't overlap
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// menu bars or left side toolbars.
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// - Canvas was placed 80px from the left of the screen.
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// Canvas.MoveTo(80, 0)
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// - A texture wants to draw at 60, 0 which would cause it to
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// overlap 20 pixels into the left toolbar. It needs to be cropped.
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// - The delta is: p.X=80 - dst.X=60 == 20
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// - Set destination X to p.X to constrain it there: 20
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// - Subtract the delta from destination W so we don't scale it.
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// - Add 20 to X of the source: the left edge of source is not visible
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if dst.X < p.X {
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// NOTE: delta is a positive number,
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// so it will add to the destination coordinates.
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delta := p.X - dst.X
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dst.X = p.X + thickness
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dst.W -= delta
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src.X += delta
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}
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if dst.Y < p.Y {
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delta := p.Y - dst.Y
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dst.Y = p.Y + thickness
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dst.H -= delta
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src.Y += delta
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}
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// Trim the destination width so it doesn't overlap the Canvas border.
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if dst.W >= S.W-thickness {
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dst.W = S.W - thickness
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}
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}
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