ebiten/internal/opengl/framebuffer.go

// 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 opengl

import (
	"errors"
	"fmt"
	"github.com/go-gl/gl"
	"github.com/hajimehoshi/ebiten/internal"
)

func orthoProjectionMatrix(left, right, bottom, top int) [4][4]float64 {
	e11 := float64(2) / float64(right-left)
	e22 := float64(2) / float64(top-bottom)
	e14 := -1 * float64(right+left) / float64(right-left)
	e24 := -1 * float64(top+bottom) / float64(top-bottom)

	return [4][4]float64{
		{e11, 0, 0, e14},
		{0, e22, 0, e24},
		{0, 0, 1, 0},
		{0, 0, 0, 1},
	}
}

type Framebuffer struct {
	framebuffer gl.Framebuffer
	width       int
	height      int
	flipY       bool
}

func NewZeroFramebuffer(width, height int) (*Framebuffer, error) {
	r := &Framebuffer{
		width:  width,
		height: height,
		flipY:  true,
	}
	return r, nil
}

func NewFramebufferFromTexture(texture *Texture) (*Framebuffer, error) {
	framebuffer, err := createFramebuffer(texture.Native())
	if err != nil {
		return nil, err
	}
	w, h := texture.Size()
	return &Framebuffer{
		framebuffer: framebuffer,
		width:       w,
		height:      h,
	}, nil
}

func (f *Framebuffer) Size() (width, height int) {
	return f.width, f.height
}

func (f *Framebuffer) Dispose() {
	f.framebuffer.Delete()
}

func createFramebuffer(nativeTexture gl.Texture) (gl.Framebuffer, error) {
	framebuffer := gl.GenFramebuffer()
	framebuffer.Bind()

	gl.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, nativeTexture, 0)
	if gl.CheckFramebufferStatus(gl.FRAMEBUFFER) != gl.FRAMEBUFFER_COMPLETE {
		return 0, errors.New("creating framebuffer failed")
	}

	return framebuffer, nil
}

func (f *Framebuffer) SetAsViewport() error {
	gl.Flush()
	f.framebuffer.Bind()
	err := gl.CheckFramebufferStatus(gl.FRAMEBUFFER)
	if err != gl.FRAMEBUFFER_COMPLETE {
		if gl.GetError() != 0 {
			return errors.New(fmt.Sprintf("glBindFramebuffer failed: %d", gl.GetError()))
		}
		return errors.New("glBindFramebuffer failed: the context is different?")
	}

	width := internal.NextPowerOf2Int(f.width)
	height := internal.NextPowerOf2Int(f.height)
	gl.Viewport(0, 0, width, height)
	return nil
}

func (f *Framebuffer) ProjectionMatrix() [4][4]float64 {
	width := internal.NextPowerOf2Int(f.width)
	height := internal.NextPowerOf2Int(f.height)
	m := orthoProjectionMatrix(0, width, 0, height)
	if f.flipY {
		m[1][1] *= -1
		m[1][3] += float64(f.height) / float64(internal.NextPowerOf2Int(f.height)) * 2
	}
	return m
}