Question

Hello Guys我是OpenGL的初学者，我正在尝试关注Android开发人员教程。但我无法看到三角形。怎么了;

我尝试在创建的曲面上创建一个三角形，并在渲染类的渲染上调用绘制方法。

三角类：

public class Triangle {
    private final String vertexShaderCode =
            "attribute vec4 vPosition;" +
            "void main() {" +
            "  gl_Position = vPosition;" +
            "}";
    private final int vertexCount = triangleCoords.length / COORDS_PER_VERTEX;
    private final int vertexStride = COORDS_PER_VERTEX * 4;
    private int mProgram,mPositionHandle,mColorHandle;
        private final String fragmentShaderCode =
            "precision mediump float;" +
            "uniform vec4 vColor;" +
            "void main() {" +
            "  gl_FragColor = vColor;" +
            "}";
    private FloatBuffer vertexBuffer;

    // 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
            -0.5f, -0.311004243f, 0.0f, // bottom left
             0.5f, -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 = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);

        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);   
    }

    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;
    }

    public void draw() {
        // Add program to OpenGL ES 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);

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

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

Answer 1

您缺少设置投影矩阵和视口的代码。您还需要调用glSwapBuffers（），除非您使用的是GLSurfaceView，它会为您执行此操作。为简单起见，您可以使用正射投影，它应该与顶点着色器中的每个vPosition相乘。

这是你可以使用和构建投影矩阵的方法：

Ortho(-1.0f, -1.0f, 1.0f, 1.0f, 1.0f, -1.0f);
glUniformMatrix4fv(iProjectionMatrixLocation, 1, GL_FALSE, (const GLfloat *)&m_mViewProj);
glViewport(0, 0, m_iWidth, m_iHeight);


...

// Construct a matrix for an orthographic projection view.
void Button::Ortho(float left, float top, float right, float bottom, float nearPlane, float farPlane)
{
    float rcplmr = 1.0f / (left - right);
    float rcpbmt = 1.0f / (bottom - top);
    float rcpnmf = 1.0f / (nearPlane - farPlane);

    m_mViewProj.f0 = -2.0f * rcplmr;
    m_mViewProj.f1 = 0.0f;
    m_mViewProj.f2 = 0.0f;
    m_mViewProj.f3 = 0.0f;
    m_mViewProj.f4 = 0.0f;
    m_mViewProj.f5 = -2.0f * rcpbmt;
    m_mViewProj.f6 = 0.0f;
    m_mViewProj.f7 = 0.0f;
    m_mViewProj.f8 = 0.0f;
    m_mViewProj.f9 = 0.0f;
    m_mViewProj.f10 = -2.0f * rcpnmf;
    m_mViewProj.f11 = 0.0f;
    m_mViewProj.f12 = (right + left) * rcplmr;
    m_mViewProj.f13 = (top + bottom) * rcpbmt;
    m_mViewProj.f14 = (nearPlane + farPlane) * rcpnmf;
    m_mViewProj.f15 = 1.0f;
}

这里的第三篇文章将有所帮助：

http://montgomery1.com/opengl/

三角形不可见OpenGLES2.0 android

1 个答案: