样例代码来源: android-openGL-canvas
OpenGL文档参考：
OpenGL文档
本文只对流程做排序以及一些简单的说明，想了解原理的请查看OpenGL相关文档，有对相应函数有疑问的可查阅上述文档。
一、创建 eglContext。EGLContext 是一个比较重的对象，所以一般只创建一次。
例子代码代码主要在 EglHelper
- egl = EGLContext.getEGL()
- 获取 eglDisplay = eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY)
- 获取 EGLConfig eglChooseConfig(..)
- eglInitialize(mEgl, mEglDisplay, mEglConfig, eglContext)
- 创建 eglContext = eglCreateContext(display, config, eglContext, attrib_list))
- 大致的相关代码
public EGLContext start(EGLContext eglContext) {
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "start() tid=" + Thread.currentThread().getId());
}
/*
* Get an EGL instance
*/
mEgl = (EGL10) EGLContext.getEGL();
/*
* Get to the default display.
*/
mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);
if (mEglDisplay == EGL10.EGL_NO_DISPLAY) {
throw new RuntimeException("eglGetDisplay failed");
}
/*
* We can now initialize EGL for that display
*/
int[] version = new int[2];
if (!mEgl.eglInitialize(mEglDisplay, version)) {
throw new RuntimeException("eglInitialize failed");
}
mEglConfig = eglConfigChooser.chooseConfig(mEgl, mEglDisplay);
/*
* Create an EGL context. We want to do this as rarely as we can, because an
* EGL context is a somewhat heavy object.
*/
mEglContext = eglContextFactory.createContext(mEgl, mEglDisplay, mEglConfig, eglContext);
if (mEglContext == null || mEglContext == EGL10.EGL_NO_CONTEXT) {
mEglContext = null;
throwEglException("createContext");
}
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "createContext " + mEglContext + " tid=" + Thread.currentThread().getId());
}
mEglSurface = null;
return mEglContext;
}
二、创建 surface
eglCreateWindowSurface(display, config, nativeWindow, surfaceAttribs)
将 context 和 surface 联系起来。
eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext)如果需要更换surface，就先destroy现在的
eglDestroySurface大致的相关代码
public boolean createSurface(Object surface) {
if (GLThread.LOG_EGL) {
Log.w("EglHelper", "createSurface() tid=" + Thread.currentThread().getId());
}
/*
* Check preconditions.
*/
if (mEgl == null) {
throw new RuntimeException("egl not initialized");
}
if (mEglDisplay == null) {
throw new RuntimeException("eglDisplay not initialized");
}
if (mEglConfig == null) {
throw new RuntimeException("mEglConfig not initialized");
}
/*
* The window size has changed, so we need to create a new
* surface.
*/
destroySurfaceImp();
/*
* Create an EGL surface we can render into.
*/
mEglSurface = eglWindowSurfaceFactory.createWindowSurface(mEgl,
mEglDisplay, mEglConfig, surface);
if (mEglSurface == null || mEglSurface == EGL10.EGL_NO_SURFACE) {
int error = mEgl.eglGetError();
if (error == EGL10.EGL_BAD_NATIVE_WINDOW) {
Log.e("EglHelper", "createWindowSurface returned EGL_BAD_NATIVE_WINDOW.");
}
return false;
}
/*
* Before we can issue GL commands, we need to make sure
* the context is current and bound to a surface.
*/
if (!mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface, mEglContext)) {
/*
* Could not make the context current, probably because the underlying
* SurfaceView surface has been destroyed.
*/
logEglErrorAsWarning("EGLHelper", "eglMakeCurrent", mEgl.eglGetError());
return false;
}
return true;
}
三、接下来就是使用vertex数据，texture数据，vertex shader, texture shader进行绘制了，这一部分是可以随时替换数据绘制新的东西的，其中比较耗性能的部分是编译链接shader的部分，所以要对编译链接部分进行缓存以保证性能。
代码主要在GLES20Canvas
vertex 数据
glGenBuffers(...)
glBindBuffer(GLES20.GL_ARRAY_BUFFER, bufferId)
glBufferData(GLES20.GL_ARRAY_BUFFER, buffer.capacity() * elementSize, buffer, GLES20.GL_STATIC_DRAW)
- 大致的相关代码
private int uploadBuffer(Buffer buffer, int elementSize) {
mGLId.glGenBuffers(1, mTempIntArray, 0);
checkError();
int bufferId = mTempIntArray[0];
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, bufferId);
checkError();
GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, buffer.capacity() * elementSize, buffer,
GLES20.GL_STATIC_DRAW);
checkError();
return bufferId;
}
编译，链接shader等
- 以两个 String 对象作为参数，分别是 vertex shader 和 fragment shader
- 编译
glCreateShader
glShaderSource
glCompileShader
private static int loadShader(int type, String shaderCode) {
// create a vertex shader type (GLES20.GL_VERTEX_SHADER)
// or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
int shader = GLES20.glCreateShader(type);
// add the source code to the shader and compile it
GLES20.glShaderSource(shader, shaderCode);
checkError();
GLES20.glCompileShader(shader);
checkError();
return shader;
}
- 链接
glCreateProgram
glAttachShader vertex
glAttachShader fragment
glLinkProgram
glGetProgramiv
private int assembleProgram(int vertexShader, int fragmentShader, ShaderParameter[] params) {
int program = GLES20.glCreateProgram();
checkError();
if (program == 0) {
throw new RuntimeException("Cannot create GL program: " + GLES20.glGetError());
}
GLES20.glAttachShader(program, vertexShader);
checkError();
GLES20.glAttachShader(program, fragmentShader);
checkError();
GLES20.glLinkProgram(program);
checkError();
int[] mLinkStatus = mTempIntArray;
GLES20.glGetProgramiv(program, GLES20.GL_LINK_STATUS, mLinkStatus, 0);
if (mLinkStatus[0] != GLES20.GL_TRUE) {
Log.e(TAG, "Could not link program: ");
Log.e(TAG, GLES20.glGetProgramInfoLog(program));
GLES20.glDeleteProgram(program);
program = 0;
}
loadHandles(params, program);
return program;
}
设定绘制区域
- glViewport(width, height)
此时就可以利用 width 和 height 来对 model view projection 矩阵进行一些初始设置了
@Override
public void setSize(int width, int height) {
mWidth = width;
mHeight = height;
GLES20.glViewport(0, 0, mWidth, mHeight);
checkError();
Matrix.setIdentityM(mMatrices, mCurrentMatrixIndex);
Matrix.orthoM(mProjectionMatrix, 0, 0, width, 0, height, -1, 1);
if (getTargetTexture() == null) {
mScreenWidth = width;
mScreenHeight = height;
Matrix.translateM(mMatrices, mCurrentMatrixIndex, 0, height, 0);
Matrix.scaleM(mMatrices, mCurrentMatrixIndex, 1, -1, 1);
}
}
对model-view矩阵进行处理(也可以不处理，看需求)
可以是平移，旋转，放缩之类的。
传入 texture, 一个带有宽高和图像数据的对象。
- glUseProgram(programId) 使用之前编译链接好的的id
- 将texture数据传入到OpenGL里的gl操作
glActiveTexture(GLES20.GL_TEXTURE0)
private void prepareTexture(BasicTexture texture, int program, ShaderParameter[] params) {
GLES20.glUseProgram(program);
checkError();
enableBlending(!texture.isOpaque() || getAlpha() < OPAQUE_ALPHA);
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
checkError();
texture.onBind(this);
GLES20.glBindTexture(texture.getTarget(), texture.getId());
checkError();
GLES20.glUniform1i(params[INDEX_TEXTURE_SAMPLER].handle, 0);
checkError();
GLES20.glUniform1f(params[INDEX_ALPHA].handle, getAlpha());
checkError();
}
glGenTextures
glBindTexture
glTexParameteri 设定相关的texture params
@Override
public void setTextureParameters(BasicTexture texture) {
int target = texture.getTarget();
GLES20.glBindTexture(target, texture.getId());
checkError();
GLES20.glTexParameteri(target, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameteri(target, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameterf(target, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
GLES20.glTexParameterf(target, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
}
- 如果bitmap的宽高是2的倍数
glBindTexture
glTexImage2D
@Override
public void initializeTexture(BasicTexture texture, Bitmap bitmap) {
int target = texture.getTarget();
GLES20.glBindTexture(target, texture.getId());
checkError();
GLUtils.texImage2D(target, 0, bitmap, 0);
}
- 如果不是2的倍数
glBindTexture
GLUtils.texSubImage2D
@Override
public void texSubImage2D(BasicTexture texture, int xOffset, int yOffset, Bitmap bitmap,
int format, int type) {
int target = texture.getTarget();
GLES20.glBindTexture(target, texture.getId());
checkError();
GLUtils.texSubImage2D(target, 0, xOffset, yOffset, bitmap, format, type);
}
glUniform1i(...) // 对shader里面的textureSampler传值，因为ActiveTexture的是Texture0，所以传0就可以了。
GLES20.glUniform1i(params[INDEX_TEXTURE_SAMPLER].handle, 0);
将vertex的值传入OpenGL
glBindBuffer
glVertexAttribPointer
glBindBuffer 0 清理
private void setPosition(ShaderParameter[] params, int offset) {
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, mBoxCoordinates);
checkError();
GLES20.glVertexAttribPointer(params[INDEX_POSITION].handle, COORDS_PER_VERTEX,
GLES20.GL_FLOAT, false, VERTEX_STRIDE, offset * VERTEX_STRIDE);
checkError();
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
checkError();
}
texture Matrix
- 利用texture的宽高设定 textureMatrix。 textureMatrix 是shader 里的一个uniform对象，用来映射从texture对应位置获取的颜色到绘制区域。例如在不进行平移旋转等情况下，第一个像素点就绘制在第一个位置。
TextureMatrixTransformer.copyTextureCoordinates(...);
TextureMatrixTransformer.convertCoordinate(...);
TextureMatrixTransformer.setTextureMatrix(...);
model view projection matrix 将这个matrix传入到OpenGL里
translateM
scaleM
multiplyMM
glUniformMatrix4fv(...)
private void setMatrix(ShaderParameter[] params, float x, float y, float width, float height) {
Matrix.translateM(mTempMatrix, 0, mMatrices, mCurrentMatrixIndex, x, y, 0f);
Matrix.scaleM(mTempMatrix, 0, width, height, 1f);
Matrix.multiplyMM(mTempMatrix, MATRIX_SIZE, mProjectionMatrix, 0, mTempMatrix, 0);
GLES20.glUniformMatrix4fv(params[INDEX_MATRIX].handle, 1, false, mTempMatrix, MATRIX_SIZE);
checkError();
}
最后就是绘制了
glEnableVertexAttribArray positionHandle
glDrawArrays
glDisableVertexAttribArray positionHandle
private void draw(ShaderParameter[] params, int type, int count, float x, float y, float width,
float height) {
setMatrix(params, x, y, width, height);
int positionHandle = params[INDEX_POSITION].handle;
GLES20.glEnableVertexAttribArray(positionHandle);
checkError();
GLES20.glDrawArrays(type, 0, count);
checkError();
GLES20.glDisableVertexAttribArray(positionHandle);
checkError();
}
四、总结
以上，说明了OpenGL绘制的三个流程。由于OpenGL是独立于语言的，这些流程不仅适用于Android，使用其它语言编写也可借鉴。从上面冗长的流程可以看到，每次要进行绘制都写那么多代码实在不经济，那么接下来的文章就会讨论如何封装以上的流程了。其实开头的github仓库里面的代码已经有封装好的类了，有需要的话可以先去看源代码。感谢阅读！
接下来可以看：
如何封装 opengl 流程
