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 (
"fmt"
"math"
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)
// GeoMDim is a dimension of a GeoM.
const GeoMDim = 3
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// A GeoM represents a matrix to transform geometry when rendering an image.
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//
// The initial value is identity.
type GeoM struct {
a_1 float64 // The actual 'a' value minus 1
b float64
c float64
d_1 float64 // The actual 'd' value minus 1
tx float64
ty float64
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}
// String returns a string representation of GeoM.
func (g *GeoM) String() string {
return fmt.Sprintf("[[%f, %f, %f], [%f, %f, %f]]", g.a_1+1, g.b, g.tx, g.c, g.d_1+1, g.ty)
}
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// Reset resets the GeoM as identity.
func (g *GeoM) Reset() {
g.a_1 = 0
g.b = 0
g.c = 0
g.d_1 = 0
g.tx = 0
g.ty = 0
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}
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// Apply pre-multiplies a vector (x, y, 1) by the matrix.
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// In other words, Apply calculates GeoM * (x, y, 1)^T.
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// The return value is x and y values of the result vector.
func (g *GeoM) Apply(x, y float64) (float64, float64) {
return (g.a_1+1)*x + g.b*y + g.tx, g.c*x + (g.d_1+1)*y + g.ty
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}
func (g *GeoM) elements32() (a, b, c, d, tx, ty float32) {
return float32(g.a_1) + 1, float32(g.b), float32(g.c), float32(g.d_1) + 1, float32(g.tx), float32(g.ty)
}
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// Element returns a value of a matrix at (i, j).
func (g *GeoM) Element(i, j int) float64 {
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switch {
case i == 0 && j == 0:
return g.a_1 + 1
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case i == 0 && j == 1:
return g.b
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case i == 0 && j == 2:
return g.tx
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case i == 1 && j == 0:
return g.c
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case i == 1 && j == 1:
return g.d_1 + 1
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case i == 1 && j == 2:
return g.ty
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default:
panic("ebiten: i or j is out of index")
}
}
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// Concat multiplies a geometry matrix with the other geometry matrix.
// This is same as multiplying the matrix other and the matrix g in this order.
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func (g *GeoM) Concat(other GeoM) {
a := (other.a_1+1)*(g.a_1+1) + other.b*g.c
b := (other.a_1+1)*g.b + other.b*(g.d_1+1)
tx := (other.a_1+1)*g.tx + other.b*g.ty + other.tx
c := other.c*(g.a_1+1) + (other.d_1+1)*g.c
d := other.c*g.b + (other.d_1+1)*(g.d_1+1)
ty := other.c*g.tx + (other.d_1+1)*g.ty + other.ty
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
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}
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// Scale scales the matrix by (x, y).
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func (g *GeoM) Scale(x, y float64) {
a := (g.a_1 + 1) * x
b := g.b * x
tx := g.tx * x
c := g.c * y
d := (g.d_1 + 1) * y
ty := g.ty * y
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
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}
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// Translate translates the matrix by (tx, ty).
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func (g *GeoM) Translate(tx, ty float64) {
g.tx += tx
g.ty += ty
}
// Rotate rotates the matrix clockwise by theta.
// The unit is radian.
func (g *GeoM) Rotate(theta float64) {
if theta == 0 {
return
}
sin, cos := math.Sincos(theta)
a := cos*(g.a_1+1) - sin*g.c
b := cos*g.b - sin*(g.d_1+1)
tx := cos*g.tx - sin*g.ty
c := sin*(g.a_1+1) + cos*g.c
d := sin*g.b + cos*(g.d_1+1)
ty := sin*g.tx + cos*g.ty
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
}
// Skew skews the matrix by (skewX, skewY). The unit is radian.
func (g *GeoM) Skew(skewX, skewY float64) {
sx := math.Tan(skewX)
sy := math.Tan(skewY)
a := (g.a_1 + 1) + g.c*sx
b := g.b + (g.d_1+1)*sx
c := (g.a_1+1)*sy + g.c
d := g.b*sy + (g.d_1 + 1)
tx := g.tx + g.ty*sx
ty := g.ty + g.tx*sy
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
}
func (g *GeoM) det2x2() float64 {
return (g.a_1+1)*(g.d_1+1) - g.b*g.c
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}
// IsInvertible returns a boolean value indicating
// whether the matrix g is invertible or not.
func (g *GeoM) IsInvertible() bool {
return g.det2x2() != 0
}
// Invert inverts the matrix.
// If g is not invertible, Invert panics.
func (g *GeoM) Invert() {
det := g.det2x2()
if det == 0 {
panic("ebiten: g is not invertible")
}
a := (g.d_1 + 1) / det
b := -g.b / det
c := -g.c / det
d := (g.a_1 + 1) / det
tx := (-(g.d_1+1)*g.tx + g.b*g.ty) / det
ty := (g.c*g.tx + -(g.a_1+1)*g.ty) / det
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
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}
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// SetElement sets an element at (i, j).
func (g *GeoM) SetElement(i, j int, element float64) {
e := element
switch {
case i == 0 && j == 0:
g.a_1 = e - 1
case i == 0 && j == 1:
g.b = e
case i == 0 && j == 2:
g.tx = e
case i == 1 && j == 0:
g.c = e
case i == 1 && j == 1:
g.d_1 = e - 1
case i == 1 && j == 2:
g.ty = e
default:
panic("ebiten: i or j is out of index")
}
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}