ebiten/internal/graphicsutil/vertices.go

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// Copyright 2017 The Ebiten Authors
//
// 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 graphicsutil
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import (
"github.com/hajimehoshi/ebiten/internal/graphics"
"github.com/hajimehoshi/ebiten/internal/opengl"
)
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var (
theVerticesBackend = &verticesBackend{}
)
type verticesBackend struct {
backend []float32
head int
}
func (v *verticesBackend) sliceForOneQuad() []float32 {
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const num = 256
size := 4 * graphics.VertexSizeInBytes() / opengl.Float.SizeInBytes()
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if v.backend == nil {
v.backend = make([]float32, size*num)
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}
s := v.backend[v.head : v.head+size]
v.head += size
if v.head+size > len(v.backend) {
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v.backend = nil
v.head = 0
}
return s
}
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func isPowerOf2(x int) bool {
return (x & (x - 1)) == 0
}
func QuadVertices(width, height int, sx0, sy0, sx1, sy1 int, a, b, c, d, tx, ty float32) []float32 {
if !isPowerOf2(width) {
panic("not reached")
}
if !isPowerOf2(height) {
panic("not reached")
}
if sx0 >= sx1 || sy0 >= sy1 {
return nil
}
if sx1 <= 0 || sy1 <= 0 {
return nil
}
wf := float32(width)
hf := float32(height)
u0, v0, u1, v1 := float32(sx0)/wf, float32(sy0)/hf, float32(sx1)/wf, float32(sy1)/hf
return quadVerticesImpl(float32(sx1-sx0), float32(sy1-sy0), u0, v0, u1, v1, a, b, c, d, tx, ty)
}
func quadVerticesImpl(x, y, u0, v0, u1, v1, a, b, c, d, tx, ty float32) []float32 {
// Specifying a range explicitly here is redundant but this helps optimization
// to eliminate boundry checks.
vs := theVerticesBackend.sliceForOneQuad()[0:24]
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ax, by, cx, dy := a*x, b*y, c*x, d*y
// Vertex coordinates
vs[0] = tx
vs[1] = ty
// Texture coordinates: first 2 values indicates the actual coodinate, and
// the second indicates diagonally opposite coodinates.
// The second is needed to calculate source rectangle size in shader programs.
vs[2] = u0
vs[3] = v0
vs[4] = u1
vs[5] = v1
// and the same for the other three coordinates
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vs[6] = ax + tx
vs[7] = cx + ty
vs[8] = u1
vs[9] = v0
vs[10] = u0
vs[11] = v1
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vs[12] = by + tx
vs[13] = dy + ty
vs[14] = u0
vs[15] = v1
vs[16] = u1
vs[17] = v0
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vs[18] = ax + by + tx
vs[19] = cx + dy + ty
vs[20] = u1
vs[21] = v1
vs[22] = u0
vs[23] = v0
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return vs
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}
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var (
quadIndices = []uint16{0, 1, 2, 1, 2, 3}
)
func QuadIndices() []uint16 {
return quadIndices
}