OpenGL ES 1.0与OpenGL ES 2.0投射和摄像视角代码区别

OpenGL ES 1.0中的投射和摄像视角

1. 投射矩阵 - 使用几何学创建一个投射矩阵，用来计算对象的坐标，以便图像被以正确的比例绘制。下面的例子展示了如何基于屏幕尺寸比例创建一个投射矩阵，然后应用到OpenGL渲染环境中。

public void onSurfaceChanged(GL10 gl, int width, int height) {
gl.glViewport(0, 0, width, height);
// make adjustments for screen ratio
float ratio = (float) width / height;
gl.glMatrixMode(GL10.GL_PROJECTION);        // set matrix to projection mode
gl.glLoadIdentity();                        // reset the matrix to its default state
gl.glFrustumf(-ratio, ratio, -1, 1, 3, 7);  // apply the projection matrix
}

2. 摄像转换矩阵 - 一旦你已经使用投射矩阵调整了坐标系统，你也必须使用一个摄像视角。下面的例子展示了如何修改onDrawFrame()方法实现应用一个模式视图，然后使用GLU.gluLookAt()功能创建一个视角转换，类似一个拍摄点。

public void onDrawFrame(GL10 gl) {
...
// Set GL_MODELVIEW transformation mode
gl.glMatrixMode(GL10.GL_MODELVIEW);
gl.glLoadIdentity();                      // reset the matrix to its default state
// When using GL_MODELVIEW, you must set the camera view
GLU.gluLookAt(gl, 0, 0, -5, 0f, 0f, 0f, 0f, 1.0f, 0.0f);
...
}

OpenGL ES 2.0中的投射和摄像视角

在ES2.0API中，先要添加一个矩阵成员到图像对象的顶点着色器中。

1. 添加矩阵到顶点着色器 - 下面的代码中包含uMVPMatrix成员，允许你应用投射和摄像视角矩阵到对象坐标中。

private final String vertexShaderCode =
// This matrix member variable provides a hook to manipulate
// the coordinates of objects that use this vertex shader
"uniform mat4 uMVPMatrix;   \n" +
"attribute vec4 vPosition;  \n" +
"void main(){               \n" +
// the matrix must be included as part of gl_Position
" gl_Position = uMVPMatrix * vPosition; \n" +
"}  \n";

2. 访问着色器矩阵 - 在顶点着色器中创建了一个钩子后，我们可以访问顶点着色器中的矩阵变量了。

public void onSurfaceCreated(GL10 unused, EGLConfig config) {
...
muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
...
}

3. 创建投射和摄像视角矩阵。

public void onSurfaceCreated(GL10 unused, EGLConfig config) {
...
// Create a camera view matrix
Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);
}
public void onSurfaceChanged(GL10 unused, int width, int height) {
GLES20.glViewport(0, 0, width, height);
float ratio = (float) width / height;
// create a projection matrix from device screen geometry
Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 3, 7);
}

4. 应用投射和摄像视角矩阵

public void onDrawFrame(GL10 unused) {
...
// Combine the projection and camera view matrices
Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0);
// Apply the combined projection and camera view transformations
GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
// Draw objects
...
}