75 lines
2.4 KiB
Go
75 lines
2.4 KiB
Go
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package pixel
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import "github.com/go-gl/mathgl/mgl32"
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// Transform holds space transformation information. Concretely, a transformation is specified by position,
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// anchor, scale and rotation.
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//
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// All points are first rotated around the anchor. Then they are multiplied by the scale. If the
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// scale factor is 2, the object becomes 2x bigger. Finally, all points are moved, so that the original
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// anchor is located precisely at the position.
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//
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// Create a Transform object with the Position function. This sets the position variable, which is the
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// most important. Then use methods, like Scale and Rotate to change scale, rotation and achor. The order
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// in which you apply these methods is irrelevant.
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//
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// pixel.Position(pixel.V(100, 100)).Rotate(math.Pi / 3).Scale(1.5)
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type Transform struct {
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pos, anc Vec
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sca, rot float64
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}
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// Position creates a Transformation object with specified position. Anchor is (0, 0), rotation is 0 and scale is 1.
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func Position(position Vec) Transform {
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return Transform{
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pos: position,
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sca: 1,
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}
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}
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// Move adds delta to position.
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func (t Transform) Move(delta Vec) Transform {
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t.pos += delta
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return t
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}
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// Anchor sets anchor. Anchor is the rotation center and will be moved to the position.
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func (t Transform) Anchor(anchor Vec) Transform {
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t.anc = anchor
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return t
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}
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// MoveAnchor adds delta to anchor.
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func (t Transform) MoveAnchor(delta Vec) Transform {
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t.anc += delta
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return t
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}
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// Scale scales the transform by the supplied factor.
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//
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// Note, that subsequent calls to this method accumulate the final scale factor. Scaling two times by 2 is equivalent
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// to scaling once by 4.
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func (t Transform) Scale(scale float64) Transform {
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t.sca *= scale
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return t
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}
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// Rotate rotates the transform by the supplied angle in radians.
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//
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// Note, that subsequent calls to this method accumulate the final rotation. Rotating two times by Pi/2 is
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// equivalent to rotating once by Pi.
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func (t Transform) Rotate(angle float64) Transform {
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t.rot += angle
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return t
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}
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// Mat3 returns a transformation matrix that satisfies previously set transform properties.
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func (t Transform) Mat3() mgl32.Mat3 {
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mat := mgl32.Ident3()
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mat = mat.Mul3(mgl32.Translate2D(float32(t.pos.X()), float32(t.pos.Y())))
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mat = mat.Mul3(mgl32.Scale2D(float32(t.sca), float32(t.sca)))
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mat = mat.Mul3(mgl32.Rotate3DZ(float32(t.rot)))
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mat = mat.Mul3(mgl32.Translate2D(float32(t.anc.X()), float32(t.anc.Y())))
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return mat
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}
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