opengl-es如何绘制纹理圆圈？

Question

我的朋友在 opengl-es 中绘制纹理圆有问题，他不能 post 他在这个网站上的报价，他让我帮他做，他会跟进post 并通过我的帐户回复。

所以，如果这个东西没有错，或者没有违反本站的条款，请帮忙。

他的报价：

opengl-es如何绘制纹理圆？

这是他的代码：

package com.test;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLUtils;

import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

class TextureBall {
    private FloatBuffer vertexBuffer; // Buffer for vertex-array
    private FloatBuffer texBuffer;    // Buffer for texture-coords-array (NEW)
    private int points=360;
    private float vertices[]={0.0f,0.0f,0.0f};
    private FloatBuffer vertBuff;

    float[] texCoords = { // Texture coords for the above face (NEW)
            0.0f, 1.0f,  // A. left-bottom (NEW)
            1.0f, 1.0f,  // B. right-bottom (NEW)
            0.0f, 0.0f,  // C. left-top (NEW)
            1.0f, 0.0f   // D. right-top (NEW)
    };
    int[] textureIDs = new int[1];   // Array for 1 texture-ID (NEW)
    public TextureBall() {

    // Setup vertex-array buffer. Vertices in float. An float has 4 bytes
        ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4);
        vbb.order(ByteOrder.nativeOrder()); // Use native byte order
        vertexBuffer = vbb.asFloatBuffer(); // Convert from byte to float
        vertexBuffer.put(vertices);         // Copy data into buffer
        vertexBuffer.position(0);           // Rewind


    }
    // Draw the shape
    public void draw(GL10 gl) {


        vertices=new float[(points+1)*3];
        for(int i=3;i<(points+1)*3;i+=3){
            double rad=(i*360/points*3)*(3.14/180);
            vertices[i]=(float)Math.cos(rad);
            vertices[i+1]=(float) Math.sin(rad);
            vertices[i+2]=0;
        }
        ByteBuffer bBuff=ByteBuffer.allocateDirect(vertices.length*4);
        bBuff.order(ByteOrder.nativeOrder());
        vertBuff=bBuff.asFloatBuffer();
        vertBuff.put(vertices);
        vertBuff.position(0);





        gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);  // Disable texture-coords-array (NEW)
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glDisable(GL10.GL_CULL_FACE);
    };

    // Load an image into GL texture
    public void loadTexture(GL10 gl, Context context) {
        gl.glGenTextures(1, textureIDs, 0); // Generate texture-ID array

        gl.glBindTexture(GL10.GL_TEXTURE_2D, textureIDs[0]);   // Bind to texture ID
    // Set up texture filters
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

    // Construct an input stream to texture image "res\drawable\nehe.png"
        InputStream istream = context.getResources().openRawResource(R.drawable.nehe);
        Bitmap bitmap;
        try {
    // Read and decode input as bitmap
            bitmap = BitmapFactory.decodeStream(istream);
        } finally {
            try {
                istream.close();
            } catch(IOException e) { }
        }

    // Build Texture from loaded bitmap for the currently-bind texture ID
        GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);
        bitmap.recycle();
    }
}

请帮他解决这个问题。

Answer 1

创建一个顶点坐标和纹理坐标数组。第一点是中心点。其他点在圆上：

vertices  = new float[(points+2) * 3];
texCoords = new float[(points+2) * 2];

vertices[0] = vertices[1] = vertices[2] = 0;
texCoords[0] = texCoords[1] = 0.5;

for(int i=0; i <= points; i ++ ){

    double rad = (i * 360.0 / points) * (3.14/180);
    vertices[(i+1)*3+0] = (float)Math.cos(rad);
    vertices[(i+1)*3+1] = (float)Math.sin(rad);
    vertices[(i+1)*3+2] = 0;

    texCoords[(i+1)*2+0] = 0.5 + 0.5 * Math.cos(rad);
    texCoords[(i+1)*2+1] = 0.5 - 0.5 * Math.sin(rad);
}

像定义顶点坐标一样定义纹理坐标的缓冲区。例如：

ByteBuffer bTBuff = ByteBuffer.allocateDirect(texCoords .length*4);
bTBuff.order(ByteOrder.nativeOrder());
texBuff = bBuff.asFloatBuffer();
texBuff.put(texCoords );
texBuff.position(0);

另见 Java Code Examples for java.nio.FloatBuffer

定义一个顶点数据数组（glVertexPointer) and texture coordinates (glTexCoordPointer）：

gl.glVertexPointer(3, 0, vertBuff); 
gl.glTexCoordPointer(2, 0, texBuff);

另见 Java Code Examples for org.lwjgl.opengl.GL11.glVertexPointer()

为顶点坐标和纹理坐标启用客户端状态（glEnableClientState）：

gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

绑定纹理并启用二维纹理 (glEnable):

gl.glBindTexture(GL10.GL_TEXTURE_2D, textureIDs[0]); 
gl.glEnable(GL10.GL_TEXTURE_2D);

另见 Java Code Examples for org.lwjgl.opengl.GL11.glEnable()

使用原始类型绘制GL_TRIANGLE_FAN and draw the circular shape by glDrawArrays

gl.glDrawArrays(GL10.GL_TRIANGLE_FAN, 0, points+2);

另见 Java Code Examples for org.lwjgl.opengl.GL11.glDrawArrays()

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