我刚开始学习OpenGL,从dev.android.com上的小教程入手。示例代码包括一个用于正方形图形的Square
类。该对象将在onSurfaceCreated()
方法中创建,并使用onDrawFrame()
每帧绘制一次。以下是Square
的示例代码(构造函数和绘图方法):
public Square() {
// initialize vertex byte buffer for shape coordinates
ByteBuffer bb = ByteBuffer.allocateDirect(squareCoords.length * 4);
bb.order(ByteOrder.nativeOrder());
vertexBuffer = bb.asFloatBuffer();
vertexBuffer.put(squareCoords);
vertexBuffer.position(0);
// initialize byte buffer for the draw list
ByteBuffer dlb = ByteBuffer.allocateDirect(drawOrder.length * 2);
dlb.order(ByteOrder.nativeOrder());
drawListBuffer = dlb.asShortBuffer();
drawListBuffer.put(drawOrder);
drawListBuffer.position(0);
// prepare shaders and OpenGL program
int vertexShader = MyGLRenderer.loadShader(
GLES20.GL_VERTEX_SHADER,
vertexShaderCode);
int fragmentShader = MyGLRenderer.loadShader(
GLES20.GL_FRAGMENT_SHADER,
fragmentShaderCode);
mProgram = GLES20.glCreateProgram(); // create empty OpenGL Program
GLES20.glAttachShader(mProgram, vertexShader); // add the vertex shader to program
GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
GLES20.glLinkProgram(mProgram); // create OpenGL program executables
}
public void draw(float[] mvpMatrix) {
// Add program to OpenGL environment
GLES20.glUseProgram(mProgram);
// get handle to vertex shader's vPosition member
mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
// Enable a handle to the triangle vertices
GLES20.glEnableVertexAttribArray(mPositionHandle);
// Prepare the triangle coordinate data
GLES20.glVertexAttribPointer(
mPositionHandle, COORDS_PER_VERTEX,
GLES20.GL_FLOAT, false,
vertexStride, vertexBuffer);
// get handle to fragment shader's vColor member
mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");
// Set color for drawing the triangle
GLES20.glUniform4fv(mColorHandle, 1, color, 0);
// get handle to shape's transformation matrix
mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
MyGLRenderer.checkGlError("glGetUniformLocation");
// Apply the projection and view transformation
GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
MyGLRenderer.checkGlError("glUniformMatrix4fv");
// Draw the square
GLES20.glDrawElements(
GLES20.GL_TRIANGLES, drawOrder.length,
GLES20.GL_UNSIGNED_SHORT, drawListBuffer);
// Disable vertex array
GLES20.glDisableVertexAttribArray(mPositionHandle);
}
我的问题是:如何在触摸事件后创建对象,而不是在
onSurfaceCreated()
中创建对象?我尝试定义一个
Square
变量,但在onSurfaceCreated()
中不初始化它,然后在绘制之前检查对象是否为空。触摸后,我调用:mSquare = new Square();
我知道这不是一个好的实现方式,但我只是想尝试一下它是否有效。我本来会创建一个可绘制元素列表,并在onDrawFrame()
方法中运行它,从列表对象调用每个draw()
。但由于这种方法会导致程序崩溃,我不知道该怎么办。