OpenGL 2.0 ES Android 绘制矩形

Question

OpenGL 2.0 ES Android 绘制矩形

3

我将遵循谷歌的教程(http://developer.android.com/training/graphics/opengl/environment.html)，并且认为我已经正确地完成了所有步骤。但是我有一个问题，三角形和矩形是不可见的，而LogCat没有显示任何错误。这是我的矩形代码：

package com.example.gameengine;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.ShortBuffer;

import android.opengl.GLES20;

/**
 * A two-dimensional square for use as a drawn object in OpenGL ES 2.0.
 */
public class GLObject {

    private final String vertexShaderCode =
            // This matrix member variable provides a hook to manipulate
            // the coordinates of the objects that use this vertex shader
            "uniform mat4 uMVPMatrix;" +
            "attribute vec4 vPosition;" +
            "void main() {" +
            // The matrix must be included as a modifier of gl_Position.
            // Note that the uMVPMatrix factor *must be first* in order
            // for the matrix multiplication product to be correct.
            "  gl_Position = uMVPMatrix * vPosition;" +
            "}";

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

    private final FloatBuffer vertexBuffer;
    private final ShortBuffer drawListBuffer;
    private final int mProgram;
    private int mPositionHandle;
    private int mColorHandle;
    private int mMVPMatrixHandle;

    // number of coordinates per vertex in this array
    static final int COORDS_PER_VERTEX = 3;
    static float squareCoords[] = {
            -0.5f,  0.5f, 0.0f,   // top left
            -0.5f, -0.5f, 0.0f,   // bottom left
             0.5f, -0.5f, 0.0f,   // bottom right
             0.5f,  0.5f, 0.0f }; // top right

    private final short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices

    private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex

    float color[] = { 0.2f, 0.709803922f, 0.898039216f, 1.0f };

    /**
     * Sets up the drawing object data for use in an OpenGL ES context.
     */
    public GLObject() {
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
        // (# of coordinate values * 4 bytes per float)
                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(
                // (# of coordinate values * 2 bytes per short)
                drawOrder.length * 2);
        dlb.order(ByteOrder.nativeOrder());
        drawListBuffer = dlb.asShortBuffer();
        drawListBuffer.put(drawOrder);
        drawListBuffer.position(0);

        // prepare shaders and OpenGL program
        int vertexShader = GLRenderer.loadShader(
                GLES20.GL_VERTEX_SHADER,
                vertexShaderCode);
        int fragmentShader = GLRenderer.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
    }

    /**
     * Encapsulates the OpenGL ES instructions for drawing this shape.
     *
     * @param mvpMatrix - The Model View Project matrix in which to draw
     * this shape.
     */
    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");
        GLRenderer.checkGlError("glGetUniformLocation");

        // Apply the projection and view transformation
        GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
        GLRenderer.checkGlError("glUniformMatrix4fv");

        // Draw the square
        GLES20.glDrawElements(
                GLES20.GL_TRIANGLES, drawOrder.length,
                GLES20.GL_UNSIGNED_SHORT, drawListBuffer);

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

}

这是我绘制矩形的方法：

GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);

        // Set the camera position (View matrix)
        Matrix.setLookAtM(mViewMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

        // Calculate the projection and view transformation
        Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0);

        // Draw square
        mSquare.draw(mMVPMatrix);

GLSurface已正确实现（我可以更改背景颜色）

- Filip

这些顶点似乎在NDC空间中，但在这个例子中，你明显有一个非恒等的ModelViewProjection矩阵。你可能只是将顶点从视图体积中转换出来了。 - Andon M. Coleman

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Prabindh · Answer 1

编辑：由于此处未使用顶点缓冲对象进行绘制，因此无需使用ELEMENT_ARRAY_BUFFER。在这种情况下，您是否尝试过为mvp指定一个单位矩阵，以显示没有任何变换的四边形？这将排除四边形根本没有被绘制而变得不可见的可能性。

这是完整的绘图代码吗？看起来您没有绑定ELEMENT_ARRAY_BUFFER，这是使用drawListBuffer索引顶点所需的。

使用以下内容，您可以为默认对象（0）启用此功能。

glBindBuffer(GL_ARRAY_BUFFER, somebufferID); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, someotherBufferID);