275 lines
7.7 KiB
Go
275 lines
7.7 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build linux darwin
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package glutil
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import (
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"encoding/binary"
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"image"
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"sync"
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"golang.org/x/mobile/f32"
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"golang.org/x/mobile/geom"
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"golang.org/x/mobile/gl"
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)
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var glimage struct {
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sync.Once
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quadXY gl.Buffer
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quadUV gl.Buffer
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program gl.Program
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pos gl.Attrib
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mvp gl.Uniform
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uvp gl.Uniform
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inUV gl.Attrib
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textureSample gl.Uniform
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}
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func glInit() {
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var err error
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glimage.program, err = CreateProgram(vertexShader, fragmentShader)
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if err != nil {
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panic(err)
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}
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glimage.quadXY = gl.CreateBuffer()
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glimage.quadUV = gl.CreateBuffer()
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gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadXY)
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gl.BufferData(gl.ARRAY_BUFFER, quadXYCoords, gl.STATIC_DRAW)
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gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadUV)
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gl.BufferData(gl.ARRAY_BUFFER, quadUVCoords, gl.STATIC_DRAW)
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glimage.pos = gl.GetAttribLocation(glimage.program, "pos")
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glimage.mvp = gl.GetUniformLocation(glimage.program, "mvp")
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glimage.uvp = gl.GetUniformLocation(glimage.program, "uvp")
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glimage.inUV = gl.GetAttribLocation(glimage.program, "inUV")
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glimage.textureSample = gl.GetUniformLocation(glimage.program, "textureSample")
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}
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// Image bridges between an *image.RGBA and an OpenGL texture.
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//
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// The contents of the embedded *image.RGBA can be uploaded as a
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// texture and drawn as a 2D quad.
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//
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// The number of active Images must fit in the system's OpenGL texture
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// limit. The typical use of an Image is as a texture atlas.
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type Image struct {
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*image.RGBA
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Texture gl.Texture
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texWidth int
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texHeight int
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}
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// NewImage creates an Image of the given size.
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//
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// Both a host-memory *image.RGBA and a GL texture are created.
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func NewImage(w, h int) *Image {
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dx := roundToPower2(w)
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dy := roundToPower2(h)
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// TODO(crawshaw): Using VertexAttribPointer we can pass texture
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// data with a stride, which would let us use the exact number of
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// pixels on the host instead of the rounded up power 2 size.
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m := image.NewRGBA(image.Rect(0, 0, dx, dy))
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glimage.Do(glInit)
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img := &Image{
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RGBA: m.SubImage(image.Rect(0, 0, w, h)).(*image.RGBA),
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Texture: gl.CreateTexture(),
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texWidth: dx,
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texHeight: dy,
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}
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// TODO(crawshaw): We don't have the context on a finalizer. Find a way.
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// runtime.SetFinalizer(img, func(img *Image) { gl.DeleteTexture(img.Texture) })
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gl.BindTexture(gl.TEXTURE_2D, img.Texture)
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gl.TexImage2D(gl.TEXTURE_2D, 0, dx, dy, gl.RGBA, gl.UNSIGNED_BYTE, nil)
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gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
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gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
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gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
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gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
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return img
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}
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func roundToPower2(x int) int {
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x2 := 1
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for x2 < x {
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x2 *= 2
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}
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return x2
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}
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// Upload copies the host image data to the GL device.
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func (img *Image) Upload() {
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gl.BindTexture(gl.TEXTURE_2D, img.Texture)
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gl.TexSubImage2D(gl.TEXTURE_2D, 0, 0, 0, img.texWidth, img.texHeight, gl.RGBA, gl.UNSIGNED_BYTE, img.Pix)
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}
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// Draw draws the srcBounds part of the image onto a parallelogram, defined by
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// three of its corners, in the current GL framebuffer.
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func (img *Image) Draw(topLeft, topRight, bottomLeft geom.Point, srcBounds image.Rectangle) {
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// TODO(crawshaw): Adjust viewport for the top bar on android?
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gl.UseProgram(glimage.program)
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{
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// We are drawing a parallelogram PQRS, defined by three of its
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// corners, onto the entire GL framebuffer ABCD. The two quads may
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// actually be equal, but in the general case, PQRS can be smaller,
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// and PQRS is not necessarily axis-aligned.
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//
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// A +---------------+ B
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// | P +-----+ Q |
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// | | | |
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// | S +-----+ R |
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// D +---------------+ C
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//
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// There are two co-ordinate spaces: geom space and framebuffer space.
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// In geom space, the ABCD rectangle is:
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//
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// (0, 0) (geom.Width, 0)
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// (0, geom.Height) (geom.Width, geom.Height)
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//
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// and the PQRS quad is:
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//
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// (topLeft.X, topLeft.Y) (topRight.X, topRight.Y)
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// (bottomLeft.X, bottomLeft.Y) (implicit, implicit)
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//
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// In framebuffer space, the ABCD rectangle is:
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//
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// (-1, +1) (+1, +1)
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// (-1, -1) (+1, -1)
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//
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// First of all, convert from geom space to framebuffer space. For
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// later convenience, we divide everything by 2 here: px2 is half of
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// the P.X co-ordinate (in framebuffer space).
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px2 := -0.5 + float32(topLeft.X/geom.Width)
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py2 := +0.5 - float32(topLeft.Y/geom.Height)
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qx2 := -0.5 + float32(topRight.X/geom.Width)
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qy2 := +0.5 - float32(topRight.Y/geom.Height)
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sx2 := -0.5 + float32(bottomLeft.X/geom.Width)
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sy2 := +0.5 - float32(bottomLeft.Y/geom.Height)
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// Next, solve for the affine transformation matrix
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// [ a00 a01 a02 ]
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// a = [ a10 a11 a12 ]
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// [ 0 0 1 ]
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// that maps A to P:
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// a × [ -1 +1 1 ]' = [ 2*px2 2*py2 1 ]'
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// and likewise maps B to Q and D to S. Solving those three constraints
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// implies that C maps to R, since affine transformations keep parallel
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// lines parallel. This gives 6 equations in 6 unknowns:
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// -a00 + a01 + a02 = 2*px2
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// -a10 + a11 + a12 = 2*py2
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// +a00 + a01 + a02 = 2*qx2
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// +a10 + a11 + a12 = 2*qy2
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// -a00 - a01 + a02 = 2*sx2
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// -a10 - a11 + a12 = 2*sy2
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// which gives:
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// a00 = (2*qx2 - 2*px2) / 2 = qx2 - px2
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// and similarly for the other elements of a.
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glimage.mvp.WriteAffine(&f32.Affine{{
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qx2 - px2,
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px2 - sx2,
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qx2 + sx2,
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}, {
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qy2 - py2,
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py2 - sy2,
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qy2 + sy2,
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}})
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}
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{
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// Mapping texture co-ordinates is similar, except that in texture
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// space, the ABCD rectangle is:
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//
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// (0,0) (1,0)
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// (0,1) (1,1)
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//
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// and the PQRS quad is always axis-aligned. First of all, convert
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// from pixel space to texture space.
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w := float32(img.texWidth)
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h := float32(img.texHeight)
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px := float32(srcBounds.Min.X-img.Rect.Min.X) / w
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py := float32(srcBounds.Min.Y-img.Rect.Min.Y) / h
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qx := float32(srcBounds.Max.X-img.Rect.Min.X) / w
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sy := float32(srcBounds.Max.Y-img.Rect.Min.Y) / h
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// Due to axis alignment, qy = py and sx = px.
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//
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// The simultaneous equations are:
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// 0 + 0 + a02 = px
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// 0 + 0 + a12 = py
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// a00 + 0 + a02 = qx
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// a10 + 0 + a12 = qy = py
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// 0 + a01 + a02 = sx = px
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// 0 + a11 + a12 = sy
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glimage.uvp.WriteAffine(&f32.Affine{{
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qx - px,
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0,
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px,
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}, {
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0,
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sy - py,
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py,
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}})
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}
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gl.ActiveTexture(gl.TEXTURE0)
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gl.BindTexture(gl.TEXTURE_2D, img.Texture)
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gl.Uniform1i(glimage.textureSample, 0)
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gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadXY)
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gl.EnableVertexAttribArray(glimage.pos)
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gl.VertexAttribPointer(glimage.pos, 2, gl.FLOAT, false, 0, 0)
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gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadUV)
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gl.EnableVertexAttribArray(glimage.inUV)
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gl.VertexAttribPointer(glimage.inUV, 2, gl.FLOAT, false, 0, 0)
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gl.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
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gl.DisableVertexAttribArray(glimage.pos)
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gl.DisableVertexAttribArray(glimage.inUV)
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}
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var quadXYCoords = f32.Bytes(binary.LittleEndian,
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-1, +1, // top left
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+1, +1, // top right
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-1, -1, // bottom left
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+1, -1, // bottom right
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)
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var quadUVCoords = f32.Bytes(binary.LittleEndian,
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0, 0, // top left
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1, 0, // top right
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0, 1, // bottom left
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1, 1, // bottom right
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)
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const vertexShader = `#version 100
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uniform mat3 mvp;
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uniform mat3 uvp;
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attribute vec3 pos;
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attribute vec2 inUV;
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varying vec2 UV;
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void main() {
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vec3 p = pos;
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p.z = 1.0;
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gl_Position = vec4(mvp * p, 1);
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UV = (uvp * vec3(inUV, 1)).xy;
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}
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`
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const fragmentShader = `#version 100
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precision mediump float;
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varying vec2 UV;
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uniform sampler2D textureSample;
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void main(){
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gl_FragColor = texture2D(textureSample, UV);
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}
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`
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