56 lines
1.6 KiB
Go
56 lines
1.6 KiB
Go
package geom
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import "image"
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// Projector is used by Box and others to accept arbitrary
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type Projector interface {
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// Sign returns a {-1, 0, 1}-valued 2D vector pointing in the direction that
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// positive Z values are projected to.
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Sign() image.Point
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// Project projects a 3D point into 2D.
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Project(Int3) image.Point
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}
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// Projection uses floats to define a projection.
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type Projection struct{ X, Y float64 }
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func (π Projection) Sign() (s image.Point) {
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return image.Pt(int(FSign(π.X)), int(FSign(π.Y)))
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}
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// Project performs a parallel projection of a 3D coordiante into 2D.
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// x projects to (x + z*π.X), and y to (y + z*π.Y)
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func (π Projection) Project(p Int3) image.Point {
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return image.Pt(
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p.X+int(π.X*float64(p.Z)),
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p.Y+int(π.Y*float64(p.Z)),
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)
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}
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// IntProjection holds an integer projection definition.
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// It is designed for projecting Z onto X and Y with integer fractions as would
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// be used in e.g. a diametric projection (IntProjection{X:0, Y:-2}).
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type IntProjection image.Point
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func (π IntProjection) Sign() image.Point { return image.Point(π) }
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// Project performs an integer parallel projection of a 3D coordinate into 2D.
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// If π.X = 0, the x returned is p.X; similarly for π.Y and y.
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// Otherwise, x projects to x + z/π.X and y projects to y + z/π.Y.
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func (π IntProjection) Project(p Int3) image.Point {
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/*
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Dividing is used because there's little reason for an isometric
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projection in a game to exaggerate the Z position.
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Integers are used to preserve "pixel perfect" calculation in case you
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are making the next Celeste.
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*/
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q := p.XY()
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if π.X != 0 {
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q.X += p.Z / π.X
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}
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if π.Y != 0 {
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q.Y += p.Z / π.Y
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}
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return q
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}
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