我试图通过不在渲染缓冲区或帧缓冲区上调用glClear来保存在Open GL ES2应用程序中在屏幕上呈现的内容。
这在物理Nook Color上运作良好。但是当在物理Nexus One（运行android 2.3.6）上运行时，我遇到的问题是缓冲区的内容在第一次渲染后出现乱码。为了便于说明，下面的屏幕显示了Nexus One和Nook Color中相同代码的外观。代码几乎是从com.example.android.apis.graphics.GLES20TriangleRenderer（8级示例源代码集）中逐字记录。
/*
* Copyright (C) 2009 The Android Open Source Project
*
* 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 com.example.android.apis.graphics;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.GLUtils;
import android.opengl.Matrix;
import android.os.SystemClock;
import android.util.Log;
import com.example.android.apis.R;
class GLES20TriangleRenderer implements GLSurfaceView.Renderer {
public GLES20TriangleRenderer(Context context) {
mContext = context;
mTriangleVertices = ByteBuffer.allocateDirect(mTriangleVerticesData.length
* FLOAT_SIZE_BYTES).order(ByteOrder.nativeOrder()).asFloatBuffer();
mTriangleVertices.put(mTriangleVerticesData).position(0);
}
public void onDrawFrame(GL10 glUnused) {
// Ignore the passed-in GL10 interface, and use the GLES20
// class's static methods instead.
GLES20.glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);
GLES20.glUseProgram(mProgram);
checkGlError("glUseProgram");
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureID);
mTriangleVertices.position(TRIANGLE_VERTICES_DATA_POS_OFFSET);
GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false,
TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
checkGlError("glVertexAttribPointer maPosition");
mTriangleVertices.position(TRIANGLE_VERTICES_DATA_UV_OFFSET);
GLES20.glEnableVertexAttribArray(maPositionHandle);
checkGlError("glEnableVertexAttribArray maPositionHandle");
GLES20.glVertexAttribPointer(maTextureHandle, 2, GLES20.GL_FLOAT, false,
TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
checkGlError("glVertexAttribPointer maTextureHandle");
GLES20.glEnableVertexAttribArray(maTextureHandle);
checkGlError("glEnableVertexAttribArray maTextureHandle");
long time = SystemClock.uptimeMillis() % 4000L;
float angle = 0.090f * ((int) time);
Matrix.setRotateM(mMMatrix, 0, angle, 0, 0, 1.0f);
Matrix.multiplyMM(mMVPMatrix, 0, mVMatrix, 0, mMMatrix, 0);
Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mMVPMatrix, 0);
GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3);
checkGlError("glDrawArrays");
}
public void onSurfaceChanged(GL10 glUnused, int width, int height) {
// Ignore the passed-in GL10 interface, and use the GLES20
// class's static methods instead.
GLES20.glViewport(0, 0, width, height);
float ratio = (float) width / height;
Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 3, 7);
}
public void onSurfaceCreated(GL10 glUnused, EGLConfig config) {
// Ignore the passed-in GL10 interface, and use the GLES20
// class's static methods instead.
mProgram = createProgram(mVertexShader, mFragmentShader);
if (mProgram == 0) {
return;
}
maPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
checkGlError("glGetAttribLocation aPosition");
if (maPositionHandle == -1) {
throw new RuntimeException("Could not get attrib location for aPosition");
}
maTextureHandle = GLES20.glGetAttribLocation(mProgram, "aTextureCoord");
checkGlError("glGetAttribLocation aTextureCoord");
if (maTextureHandle == -1) {
throw new RuntimeException("Could not get attrib location for aTextureCoord");
}
muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
checkGlError("glGetUniformLocation uMVPMatrix");
if (muMVPMatrixHandle == -1) {
throw new RuntimeException("Could not get attrib location for uMVPMatrix");
}
/*
* Create our texture. This has to be done each time the
* surface is created.
*/
int[] textures = new int[1];
GLES20.glGenTextures(1, textures, 0);
mTextureID = textures[0];
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureID);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER,
GLES20.GL_NEAREST);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D,
GLES20.GL_TEXTURE_MAG_FILTER,
GLES20.GL_LINEAR);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S,
GLES20.GL_REPEAT);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T,
GLES20.GL_REPEAT);
InputStream is = mContext.getResources()
.openRawResource(R.raw.robot);
Bitmap bitmap;
try {
bitmap = BitmapFactory.decodeStream(is);
} finally {
try {
is.close();
} catch(IOException e) {
// Ignore.
}
}
GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);
bitmap.recycle();
Matrix.setLookAtM(mVMatrix, 0, 0, 0, -5, 0f, 0f, 0f, 0f, 1.0f, 0.0f);
}
private int loadShader(int shaderType, String source) {
int shader = GLES20.glCreateShader(shaderType);
if (shader != 0) {
GLES20.glShaderSource(shader, source);
GLES20.glCompileShader(shader);
int[] compiled = new int[1];
GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, compiled, 0);
if (compiled[0] == 0) {
Log.e(TAG, "Could not compile shader " + shaderType + ":");
Log.e(TAG, GLES20.glGetShaderInfoLog(shader));
GLES20.glDeleteShader(shader);
shader = 0;
}
}
return shader;
}
private int createProgram(String vertexSource, String fragmentSource) {
int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexSource);
if (vertexShader == 0) {
return 0;
}
int pixelShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentSource);
if (pixelShader == 0) {
return 0;
}
int program = GLES20.glCreateProgram();
if (program != 0) {
GLES20.glAttachShader(program, vertexShader);
checkGlError("glAttachShader");
GLES20.glAttachShader(program, pixelShader);
checkGlError("glAttachShader");
GLES20.glLinkProgram(program);
int[] linkStatus = new int[1];
GLES20.glGetProgramiv(program, GLES20.GL_LINK_STATUS, linkStatus, 0);
if (linkStatus[0] != GLES20.GL_TRUE) {
Log.e(TAG, "Could not link program: ");
Log.e(TAG, GLES20.glGetProgramInfoLog(program));
GLES20.glDeleteProgram(program);
program = 0;
}
}
return program;
}
private void checkGlError(String op) {
int error;
while ((error = GLES20.glGetError()) != GLES20.GL_NO_ERROR) {
Log.e(TAG, op + ": glError " + error);
throw new RuntimeException(op + ": glError " + error);
}
}
private static final int FLOAT_SIZE_BYTES = 4;
private static final int TRIANGLE_VERTICES_DATA_STRIDE_BYTES = 5 * FLOAT_SIZE_BYTES;
private static final int TRIANGLE_VERTICES_DATA_POS_OFFSET = 0;
private static final int TRIANGLE_VERTICES_DATA_UV_OFFSET = 3;
private final float[] mTriangleVerticesData = {
// X, Y, Z, U, V
-1.0f, -0.5f, 0, -0.5f, 0.0f,
1.0f, -0.5f, 0, 1.5f, -0.0f,
0.0f, 1.11803399f, 0, 0.5f, 1.61803399f };
private FloatBuffer mTriangleVertices;
private final String mVertexShader =
"uniform mat4 uMVPMatrix;\n" +
"attribute vec4 aPosition;\n" +
"attribute vec2 aTextureCoord;\n" +
"varying vec2 vTextureCoord;\n" +
"void main() {\n" +
" gl_Position = uMVPMatrix * aPosition;\n" +
" vTextureCoord = aTextureCoord;\n" +
"}\n";
private final String mFragmentShader =
"precision mediump float;\n" +
"varying vec2 vTextureCoord;\n" +
"uniform sampler2D sTexture;\n" +
"void main() {\n" +
" gl_FragColor = texture2D(sTexture, vTextureCoord);\n" +
"}\n";
private float[] mMVPMatrix = new float[16];
private float[] mProjMatrix = new float[16];
private float[] mMMatrix = new float[16];
private float[] mVMatrix = new float[16];
private int mProgram;
private int mTextureID;
private int muMVPMatrixHandle;
private int maPositionHandle;
private int maTextureHandle;
private Context mContext;
private static String TAG = "GLES20TriangleRenderer";
}
不同之处在于我删除了glClear调用，因此它变成了这样：
public void onDrawFrame(GL10 glUnused) {
// Ignore the passed-in GL10 interface, and use the GLES20
// class's static methods instead.
//GLES20.glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT);// | GLES20.GL_COLOR_BUFFER_BIT);
该代码基本上旋转了中心的矩形。我还尝试渲染到纹理渲染缓冲区，然后渲染渲染缓冲区纹理并遇到相同的结果（渲染缓冲区在第一次调用GLES20.glDrawArrays后出现乱码，结果看起来与错误的截图非常相似）。
我是ES2的新手。我究竟做错了什么？
糟糕（在Nexus One上）：http://www.putpix.com/b/files/2849/devicebad.png
好（Nook Color）：http://www.putpix.com/b/files/2849/devicegood.png
答案 0 :(得分：0)
如果您不打电话，则结果未定义。
特别是，屏幕通常是双缓冲的，因此您的程序将在不同时间看到多个缓冲区。缓冲区永远也没有义务与之前见过的相同。
