java - 尝试使用 Android 显示 openGL 图形

Question

我一直在关注向您展示如何使用 Android 显示 openGL 图形的 Android 文档。我很确定我已经正确地遵循了代码，但没有显示任何内容。这是我的代码:

OpenGLES20Activity.java

import javax.microedition.khronos.opengles.GL10;
import android.app.Activity;
import android.content.Context;
import android.opengl.EGLConfig;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.os.Bundle;

public class OpenGLES20Activity extends Activity {

    private GLSurfaceView mGLView;
    private MyGLRenderer renderer;
    private static Triangle mTriangle;
    private static Square mSquare;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Create a GLSurfaceView instance and set it
        // as the ContentView for this Activity.
        mGLView = new MyGLSurfaceView(this);
        setContentView(mGLView);

    }

    class MyGLSurfaceView extends GLSurfaceView {

        public MyGLSurfaceView(Context context){
            super(context);

            // Create an OpenGL ES 2.0 context
            setEGLContextClientVersion(2);

            // Set the Renderer for drawing on the GLSurfaceView
            renderer = new MyGLRenderer();
            setRenderer(renderer);
        }
    }

    public static class MyGLRenderer implements GLSurfaceView.Renderer {

        public void onSurfaceCreated(GL10 unused, EGLConfig config) {

        }

        public void onDrawFrame(GL10 unused) {
            // Redraw background color
            GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
            mTriangle.draw();
        }

        public void onSurfaceChanged(GL10 unused, int width, int height) {
            GLES20.glViewport(0, 0, width, height);
        }

        @Override
        public void onSurfaceCreated(GL10 gl,
                javax.microedition.khronos.egl.EGLConfig config) {
            // Set the background frame color
            GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
            // initialize a triangle
            mTriangle = new Triangle();
        }

        public 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);
            GLES20.glCompileShader(shader);

            return shader;
        }

    }

}

三角形.java

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import android.opengl.GLES20;
import com.example.test3d.OpenGLES20Activity.MyGLRenderer;

public class Triangle {

    private FloatBuffer vertexBuffer;
    int mProgram;
    private final String vertexShaderCode =
            "attribute vec4 vPosition;" +
            "void main() {" +
            "  gl_Position = vPosition;" +
            "}";

        private final String fragmentShaderCode =
            "precision mediump float;" +
            "uniform vec4 vColor;" +
            "void main() {" +
            "  gl_FragColor = vColor;" +
            "}";

    // number of coordinates per vertex in this array
    static final int COORDS_PER_VERTEX = 3;
    static float triangleCoords[] = {   // in counterclockwise order:
             0.0f,  0.622008459f, 0.0f, // top
             0f, 0.311004243f, 0.0f, // bottom left
             0f, 0.311004243f, 0.0f  // bottom right
    };

    // Set color with red, green, blue and alpha (opacity) values
    float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };



    public Triangle() {
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
                // (number of coordinate values * 4 bytes per float)
                triangleCoords.length * 4);
        // use the device hardware's native byte order
        bb.order(ByteOrder.nativeOrder());

        // create a floating point buffer from the ByteBuffer
        vertexBuffer = bb.asFloatBuffer();
        // add the coordinates to the FloatBuffer
        vertexBuffer.put(triangleCoords);
        // set the buffer to read the first coordinate
        vertexBuffer.position(0);

        int vertexShader = MyGLRenderer.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = MyGLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
        int mProgram = GLES20.glCreateProgram();             // create empty OpenGL ES Program
        GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
        GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
        GLES20.glLinkProgram(mProgram);                  // creates OpenGL ES program executables
    }

    public void draw() {
        int vertexStride = 10;
        int vertexCount = 10;
        // Add program to OpenGL ES environment
        GLES20.glUseProgram(mProgram);

        // get handle to vertex shader's vPosition member
        int 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
        int mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

        // Set color for drawing the triangle
        GLES20.glUniform4fv(mColorHandle, 1, color, 0);

        // Draw the triangle
        GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);

        // Disable vertex array
        GLES20.glDisableVertexAttribArray(mPositionHandle);
    }
}

---

我还在 list 文件中指定:

<uses-feature android:glEsVersion="0x00020000" android:required="true" />

编辑:明确地说，我根本没有收到任何错误。我的屏幕是黑色的，而且一直是黑色。我已经使用了一些打印语句并且我已经确认正在调用 Triangle.draw() 。所以我的猜测是绘图实现是错误的，但我遵循了文档，所以可能是其他原因。感谢您的帮助。

Answer 1

我看到两个主要问题。首先，你的三角坐标:

static float triangleCoords[] = {   // in counterclockwise order:
     0.0f,  0.622008459f, 0.0f, // top
     0f, 0.311004243f, 0.0f, // bottom left
     0f, 0.311004243f, 0.0f  // bottom right
};

第二个和第三个顶点的坐标相同。具有两个相同顶点的三角形是退化的，不会渲染任何像素。

然后这些值看起来有问题:

int vertexStride = 10;
int vertexCount = 10;

每个顶点有 3 个 float ，所以 vertexStride 应该是 3 * sizeof(float)，也就是 12。我只看到 3 个顶点，所以 vertexCount 应该是 3。