ebiten/internal/graphics/framebuffer.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 graphics
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import (
"github.com/hajimehoshi/ebiten/internal/opengl"
"github.com/hajimehoshi/ebiten/internal/web"
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)
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// orthoProjectionMatrix returns an orthogonal projection matrix for OpenGL.
//
// The matrix converts the coodinates (left, bottom) - (right, top) to the normalized device coodinates (-1, -1) - (1, 1).
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func orthoProjectionMatrix(left, right, bottom, top int) []float32 {
e11 := 2 / float32(right-left)
e22 := 2 / float32(top-bottom)
e14 := -1 * float32(right+left) / float32(right-left)
e24 := -1 * float32(top+bottom) / float32(top-bottom)
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return []float32{
e11, 0, 0, 0,
0, e22, 0, 0,
0, 0, 1, 0,
e14, e24, 0, 1,
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}
}
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// framebuffer is a wrapper of OpenGL's framebuffer.
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type framebuffer struct {
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native opengl.Framebuffer
flipY bool
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proMatrix []float32
width int
height int
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}
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// newFramebufferFromTexture creates a framebuffer from the given texture.
func newFramebufferFromTexture(texture *texture, width, height int) (*framebuffer, error) {
native, err := opengl.GetContext().NewFramebuffer(opengl.Texture(texture.native))
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if err != nil {
return nil, err
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}
return &framebuffer{
native: native,
width: width,
height: height,
}, nil
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}
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// newScreenFramebuffer creates a framebuffer for the screen.
func newScreenFramebuffer(width, height int) *framebuffer {
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return &framebuffer{
native: opengl.GetContext().ScreenFramebuffer(),
flipY: true,
width: width,
height: height,
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}
}
// defaultViewportSize is the default size (width or height) of viewport.
//
// defaultViewportSize also represents the maximum size of a framebuffer
// and of an Image (it is used to declare MaxImageSize).
//
// For portability reasons it must be a power of two.
const defaultViewportSize = 8192
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// viewportSize returns the viewport size of the framebuffer.
func (f *framebuffer) viewportSize() (int, int) {
// On some browsers, viewport size must be within the framebuffer size.
// e.g. Edge (#71), Chrome on GPD Pocket (#420)
if web.IsBrowser() {
return f.width, f.height
}
// If possible, always use the same viewport size to reduce draw calls.
return defaultViewportSize, defaultViewportSize
}
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// setAsViewport sets the framebuffer as the current viewport.
func (f *framebuffer) setAsViewport() {
w, h := f.viewportSize()
opengl.GetContext().SetViewport(f.native, w, h)
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}
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// projectionMatrix returns a projection matrix of the framebuffer.
//
// A projection matrix converts the coodinates on the framebuffer
// (0, 0) - (viewport width, viewport height)
// to the normalized device coodinates (-1, -1) - (1, 1) with adjustment.
func (f *framebuffer) projectionMatrix() []float32 {
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if f.proMatrix != nil {
return f.proMatrix
}
w, h := f.viewportSize()
m := orthoProjectionMatrix(0, w, 0, h)
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f.proMatrix = m
return f.proMatrix
}