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geom.go
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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.
package ebiten
import (
"math"
)
// GeoMDim is a dimension of a GeoM.
const GeoMDim = 3
// A GeoM represents a matrix to transform geometry when rendering an image.
//
// The initial value is identity.
type GeoM struct {
initialized bool
es [GeoMDim - 1][GeoMDim]float64
}
func (g *GeoM) dim() int {
return GeoMDim
}
func (g *GeoM) initialize() {
g.initialized = true
g.es[0][0] = 1
g.es[1][1] = 1
}
// Element returns a value of a matrix at (i, j).
func (g *GeoM) Element(i, j int) float64 {
if !g.initialized {
if i == j {
return 1
}
return 0
}
return g.es[i][j]
}
// Concat multiplies a geometry matrix with the other geometry matrix.
func (g *GeoM) Concat(other GeoM) {
if !g.initialized {
g.initialize()
}
result := GeoM{}
mul(&other, g, &result)
*g = result
}
// Add adds a geometry matrix with the other geometry matrix.
func (g *GeoM) Add(other GeoM) {
if !g.initialized {
g.initialize()
}
result := GeoM{}
add(&other, g, &result)
*g = result
}
func (g *GeoM) Scale(x, y float64) {
if !g.initialized {
g.initialize()
}
for i := 0; i < GeoMDim; i++ {
g.es[0][i] *= x
g.es[1][i] *= y
}
}
func (g *GeoM) Translate(tx, ty float64) {
if !g.initialized {
g.initialize()
}
g.es[0][2] += tx
g.es[1][2] += ty
}
func (g *GeoM) Rotate(theta float64) {
g.Concat(RotateGeo(theta))
}
// SetElement sets an element at (i, j).
func (g *GeoM) SetElement(i, j int, element float64) {
if !g.initialized {
g.initialize()
}
g.es[i][j] = element
}
// 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},
},
}
}
// 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},
},
}
}
// RotateGeo returns a matrix that rotates a geometry matrix by theta.
func RotateGeo(theta float64) GeoM {
sin, cos := math.Sincos(theta)
return GeoM{
initialized: true,
es: [2][3]float64{
{cos, -sin, 0},
{sin, cos, 0},
},
}
}