如何在 opengles 2.0 中用图像填充多边形 android

Question

我是 android opengl 的新手 development.I 想在 android 中使用 opengl-es 2.0 用图像填充多边形，如下所示。我可以画正方形、三角形，但不能用重复的图像填充它。有知道的请帮帮我

Square.java

public class Square {

private final String vertexShaderCode =
        "uniform mat4 uMVPMatrix;" +
        "attribute vec4 vPosition;" +
        "attribute vec2 a_TextureCoordinates;" +
        "varying vec2 v_TextureCoordinates;" +
        "void main() {" +                       
        "  gl_Position = uMVPMatrix * vPosition;" +
        " v_TextureCoordinates = a_TextureCoordinates;" +
        "}";      
private final String fragmentShaderCode =
        "precision mediump float;" +
        "uniform sampler2D u_TextureUnit;"+
        "varying vec2 v_TextureCoordinates;" +
        "void main() {" +
        "   gl_FragColor = texture2D(u_TextureUnit, v_TextureCoordinates);" +
        "}"; 
private final FloatBuffer vertexBuffer;
private final FloatBuffer textureBuffer;
private final ShortBuffer drawListBuffer;
private final int mProgram;
private int mPositionHandle;
private int mColorHandle;
private int mMVPMatrixHandle;
static final int COORDS_PER_VERTEX = 3;
static float squareCoords[] = {

     -1.0f,  1.0f, 0.0f,   // top left
     1.0f, 1.0f, 0.0f,  // top right
     1.0f, -1.0f, 0.0f,   // bottom right
     -1.0f, -1.0f, 0.0f   // bottom left
     };

final float[] previewTextureCoordinateData =
    {
        0.0f,0.0f, // top left
        1.0f,0.0f, // Top-right
        1.0f,1.0f, // Bottom-right          
        0.0f,1.0f,  // Bottom-left
    };
private int textureDataHandle;
private int textureUniformHandle;
private int textureCoordinateHandle;

private final short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; 
float color[] = { 0.2f, 0.709803922f, 0.898039216f, 1.0f };
private int loadTexture(final Context context, final int resourceId){    final int[] textureHandle = new int[1];

GLES20.glGenTextures(1, textureHandle, 0);

if (textureHandle[0] != 0)
{
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inScaled = false;   // No pre-scaling

    // Read in the resource
    final Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), resourceId, options);

    // Bind to the texture in OpenGL
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureHandle[0]);

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GLES20.GL_REPEAT);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GLES20.GL_REPEAT);

    // Set filtering
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);

    // Load the bitmap into the bound texture.
    GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);

    // Recycle the bitmap, since its data has been loaded into OpenGL.
    bitmap.recycle();
}

if (textureHandle[0] == 0)
{
    throw new RuntimeException("Error loading texture.");
}

return textureHandle[0];}

 public Square(Context c) {
    // 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);

    ByteBuffer texCoordinates = ByteBuffer.allocateDirect(previewTextureCoordinateData.length * 4);
    texCoordinates.order(ByteOrder.nativeOrder());
    textureBuffer = texCoordinates.asFloatBuffer();
    textureBuffer.put(previewTextureCoordinateData);
    textureBuffer.position(0);


    // prepare shaders and OpenGL program
    int vertexShader = MyGLRenderer.loadShader(
            GLES20.GL_VERTEX_SHADER,
            vertexShaderCode);
    int fragmentShader = MyGLRenderer.loadShader(
            GLES20.GL_FRAGMENT_SHADER,
            fragmentShaderCode);

    textureDataHandle = loadTexture(c, R.drawable.air_hockey_surface);

    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
}

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);

    textureCoordinateHandle = GLES20.glGetAttribLocation(mProgram, "a_TextureCoordinates");
    GLES20.glVertexAttribPointer(textureCoordinateHandle, 2, GLES20.GL_FLOAT, false, 
            0, textureBuffer);
    GLES20.glEnableVertexAttribArray(textureCoordinateHandle);

    textureUniformHandle = GLES20.glGetUniformLocation(mProgram, "u_TextureUnit");
    MyGLRenderer.checkGlError("glGetUniformLocation");
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureDataHandle);
    GLES20.glUniform1i(textureUniformHandle, 0);      

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

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

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

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

Answer 1

如果你想让纹理重复你需要设置这样的纹理坐标。纹理坐标是纹理中的相对像素位置，其中 (0.0, 0,0) 是图像的左上角位置，(1.0, 1.0) 是右下角。现在无论顶点坐标如何，显示的纹理部分将始终相同。那么在你的情况下

final float[] previewTextureCoordinateData =
    {
        0.0f,0.0f, // top left
        1.0f,0.0f, // Top-right
        1.0f,1.0f, // Bottom-right          
        0.0f,1.0f,  // Bottom-left
    };

表示您将在对象上绘制整个纹理。要使其在每个维度中重复例如 3 次，您需要将这些相乘：

final float[] previewTextureCoordinateData =
    {
        0.0f,0.0f, // top left
        1.0f*3.0,0.0f, // Top-right
        1.0f*3.0,1.0f*3.0, // Bottom-right          
        0.0f,1.0f*3.0,  // Bottom-left
    };

纹理上已经启用了重复，所以应该是这样。

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