Android OpenGL ES 2,绘制正方形

Question

编辑:问题解决了! 所以我一直在浏览Android的官方OpenGL ES 2教程,并且我已经完成了涉及绘制形状的部分,但我似乎无法找到一个正方形.它绘制了一个直角三角形.

我已经包含了我用来定义和绘制形状的代码,几乎完全从教程中复制了.Renderer类只是创建这个形状的实例并调用draw方法.

由于某种原因,本教程没有给出vertexStride和vertexCount的值/声明,所以我在那里的那些是有根据的猜测.我已经为vertexCount(1到12)尝试了几个值,但都没有工作.

提前致谢.

            public class Square {

                private FloatBuffer vertexBuffer;
                private ShortBuffer drawListBuffer;

                // 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 short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices
                float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };


                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;" +
                    "}";

                int mProgram;

                static final int vertexStride = COORDS_PER_VERTEX * 4;
                static final int vertexCount = 4;

                public Square() {
                    // initialize vertex byte buffer for shape coordinates
                    ByteBuffer bb = ByteBuffer.allocateDirect(squareCoords.length * 4); // (# of coordinate values * 4 bytes per float)
                    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); // (# of coordinate values * 2 bytes per short)
                    dlb.order(ByteOrder.nativeOrder());
                    drawListBuffer = dlb.asShortBuffer();
                    drawListBuffer.put(drawOrder);
                    drawListBuffer.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);                  // creates OpenGL ES program executables
                }

                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
                    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);
                }
            }

Answer 1

vertexCount = squareCoords.length/COORDS_PER_VERTEX; //Vertex count is the array divided by the size of the vertex ex. (x,y) or (x,y,z) 
vertexStride = COORDS_PER_VERTEX * 4;                //4 are how many bytes in a float

如果这对你有用,请告诉我,祝你好运.

我想你也错过了ModelViewProjection用于将3D空间转换为2D屏幕空间的Matrix.mvpMatrix应该通过绘制函数传入draw(float[] mvpMatrix) 忘记提及你也应该使用DrawElements(...)(在示例中使用)如果你不需要计数或步幅,只需要idicies数组和绘图缓冲区的长度.

    // Get handle to shape's transformation matrix
    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");

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

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

Answer 2

本教程缺少一些步骤:广场的最终代码在这里.

该示例旨在使用glDrawElements而不是glDrawArrays由线的存在表示:private short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices.

此数组指定2个三角形的所需顶点.0,1和2为第一个.第二个是0,2和3.GL_TRANGLE_FAN恰好工作,因为它将使用缓冲区中的第一个顶点,前一个三角形中使用的最后一个顶点和下一个顶点绘制下一个三角形.对于第二个三角形,这是0,2和3.然后0,3和4等.如果顶点2是5,5,顶点3是-5,5,则得到的扇形不是正方形.

替换这些行:

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

用这些:

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