ebiten/geom.go

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// Copyright 2014 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
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package ebiten
import (
"math"
)
// GeoMDim is a dimension of a GeoM.
const GeoMDim = 3
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var geoMI = GeoM{
initialized: true,
es: [2][3]float64{
{1, 0, 0},
{0, 1, 0},
},
}
// A GeoM represents a matrix to transform geometry when rendering an image.
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//
// The initial value is identity.
type GeoM struct {
initialized bool
es [GeoMDim - 1][GeoMDim]float64
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}
func (g GeoM) dim() int {
return GeoMDim
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}
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// Element returns a value of a matrix at (i, j).
func (g GeoM) Element(i, j int) float64 {
if !g.initialized {
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if i == j {
return 1
}
return 0
}
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return g.es[i][j]
}
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// Concat multiplies a geometry matrix with the other geometry matrix.
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func (g *GeoM) Concat(other GeoM) {
if !g.initialized {
*g = geoMI
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}
result := GeoM{}
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mul(&other, g, &result)
*g = result
}
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// Add adds a geometry matrix with the other geometry matrix.
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func (g *GeoM) Add(other GeoM) {
if !g.initialized {
*g = geoMI
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}
result := GeoM{}
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add(&other, g, &result)
*g = result
}
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// SetElement sets an element at (i, j).
func (g *GeoM) SetElement(i, j int, element float64) {
if !g.initialized {
*g = geoMI
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}
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g.es[i][j] = element
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}
// ScaleGeo returns a matrix that scales a geometry matrix by (x, y).
func ScaleGeo(x, y float64) GeoM {
return GeoM{
initialized: true,
es: [2][3]float64{
{x, 0, 0},
{0, y, 0},
},
}
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}
// TranslateGeo returns a matrix taht translates a geometry matrix by (tx, ty).
func TranslateGeo(tx, ty float64) GeoM {
return GeoM{
initialized: true,
es: [2][3]float64{
{1, 0, tx},
{0, 1, ty},
},
}
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}
// RotateGeo returns a matrix that rotates a geometry matrix by theta.
func RotateGeo(theta float64) GeoM {
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sin, cos := math.Sincos(theta)
return GeoM{
initialized: true,
es: [2][3]float64{
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{cos, -sin, 0},
{sin, cos, 0},
},
}
}