46 lines
1 KiB
Go
46 lines
1 KiB
Go
package engine
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import (
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"encoding/gob"
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"fmt"
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)
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var _ interface {
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Prepper
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Scanner
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Transformer
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} = &Parallax{}
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func init() {
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gob.Register(&Parallax{})
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}
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// Parallax is a container that translates based on the position of a
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// camera, intended to produce a "parallax" like effect.
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type Parallax struct {
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CameraID string
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Factor float64 // how much to translate in response to the camera
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Child interface{}
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camera *Camera
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}
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// Prepare obtains a reference to the camera.
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func (p *Parallax) Prepare(game *Game) error {
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c, ok := game.Component(p.CameraID).(*Camera)
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if !ok {
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return fmt.Errorf("component %q type != *Camera", p.CameraID)
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}
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p.camera = c
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return nil
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}
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// Scan returns the child component.
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func (p *Parallax) Scan() []interface{} { return []interface{}{p.Child} }
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// Transform returns a GeoM translation of Factor * camera.Centre.
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func (p *Parallax) Transform(pt Transform) (tf Transform) {
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x, y := cfloat(p.camera.Centre)
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tf.Opts.GeoM.Translate(x*p.Factor, y*p.Factor)
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return tf.Concat(pt)
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}
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