Question

我一直在开发一个openGL ES 2.0 Android项目。我的目标是创建一个圆圈。从我从网上获得的帮助，我设法运行这个代码，假设在视图中给出一个圆圈，但我得到了一个椭圆形。我尝试了很多方法让它成为循环。任何帮助都要赞赏

由于

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

import android.opengl.GLES20;
import android.util.Log;

public class Circle {

private int mProgram, mPositionHandle, mColorHandle, mMVPMatrixHandle;
private FloatBuffer mVertexBuffer;
private float vertices[] = new float[364 * 3];
float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

private final String vertexShaderCode = "uniform mat4 uMVPMatrix;"
        + "attribute vec4 vPosition;" + "void main() {"
        + "  gl_Position = uMVPMatrix * vPosition;" + "}";

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

Circle() {
    vertices[0] = 0;
    vertices[1] = 0;
    vertices[2] = 0;

    for (int i = 1; i < 364; i++) {
        vertices[(i * 3) + 0] = (float) (0.5 * Math.cos((3.14 / 180)
                * (float) i) + vertices[0]);
        vertices[(i * 3) + 1] = (float) (0.5 * Math.sin((3.14 / 180)
                * (float) i) + vertices[1]);
        vertices[(i * 3) + 2] = 0;
    }

    Log.v("Thread", "" + vertices[0] + "," + vertices[1] + ","
            + vertices[2]);
    ByteBuffer vertexByteBuffer = ByteBuffer
            .allocateDirect(vertices.length * 4);
    vertexByteBuffer.order(ByteOrder.nativeOrder());
    mVertexBuffer = vertexByteBuffer.asFloatBuffer();
    mVertexBuffer.put(vertices);
    mVertexBuffer.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) {

    int shader = GLES20.glCreateShader(type);
    GLES20.glShaderSource(shader, shaderCode);
    GLES20.glCompileShader(shader);
    return shader;
}

public void draw(float[] mvpMatrix) {

    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, 3, GLES20.GL_FLOAT,
            false, 12, mVertexBuffer);

    // 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);

    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");

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

    // Draw the triangle
    GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 364);

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

}

}

我得到的输出就是这个

enter image description here

Answer 1

顶点坐标跨越一个（标准化的）-1到+1的范围 - 看起来你正在生成从-0.5到+0.5的顶点。

现在，GL引擎在哪里绘制？到窗口系统提供的缓冲区 - 在这种情况下是Android窗口系统。 Android窗口系统（即最低级别的Linux内核显示驱动程序）提供了一个宽度x高度为480x640的缓冲区（屏幕截图显示宽度＆lt; height）。因此，屏幕上绘制的圆圈宽度为0.5 * 480，但高度为0.5 * 640，因此呈椭圆形。

您必须按（屏幕宽度/屏幕高度）的比例缩小y坐标才能得到真正的圆。您可以在应用程序中使用egl API或Android API来获取它。

如何将椭圆转换为圆形openGL ES2.0 Android

1 个答案: