android - GLES20 纹理在某些设备上不起作用

Question

我尝试在 Android's example OpenGL 2.0 project 之上添加一个相当简单的扩展以便为基本形状添加纹理。这似乎非常简单，但在某些设备(Samsung Nexus S、LG Optimus 3D、Samsung Galaxy S)上，纹理无法渲染。

这实际上是我在一个更大的项目中遇到的问题，但我能够使用下面的简单项目重现该问题，希望这里有人知道我的代码在哪里出现问题，或者如何为这些设备专门构建 GL 纹理(设备可能存在问题)。

要了解如何使用此对象:在 GLSurfaceView.Renderer 的 onSurfaceCreated 方法中，我实例化一个 Square() 对象，并在 onDrawFrame 中 方法 我正在调用 Square 的 draw() 方法。然而，处理纹理的所有相关代码都应该出现在这个 Square 类中，它与 Google 自己的示例几乎完全相同。

非常感谢任何尝试此方法的人。

class Square {

private final String vertexShaderCode =
    // This matrix member variable provides a hook to manipulate
    // the coordinates of the objects that use this vertex shader
    "uniform mat4 uMVPMatrix;" +

    "attribute vec4 vPosition;" +
    "attribute vec2 a_TexCoordinate;" +

    "varying vec2 v_TexCoordinate;" +

    "void main() {" +
    // the matrix must be included as a modifier of gl_Position
    "  gl_Position = vPosition * uMVPMatrix;" +
    "  v_TexCoordinate = a_TexCoordinate;" +
    "}";

private final String fragmentShaderCode =
    "precision mediump float;" +

    "uniform sampler2D u_Texture;" +

    "varying vec2 v_TexCoordinate;" +

    "void main() {" +
    "  gl_FragColor = texture2D(u_Texture, v_TexCoordinate);" +
    "}";

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;

// 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

final float[] previewTextureCoordinateData =
    {
        0.0f, 1.0f,
        0.0f, 0.0f, 
        1.0f, 1.0f,
        1.0f, 0.0f
    };

private int textureDataHandle;
private int textureUniformHandle;
private int textureCoordinateHandle;

private final short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices

private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex

// Set color with red, green, blue and alpha (opacity) values
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]);

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

        // 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 context) {
    // 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(context, R.drawable.color_texture);

    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_TexCoordinate");
    GLES20.glVertexAttribPointer(textureCoordinateHandle, 2, GLES20.GL_FLOAT, false, 
            0, textureBuffer);
    GLES20.glEnableVertexAttribArray(textureCoordinateHandle);

    textureUniformHandle = GLES20.glGetUniformLocation(mProgram, "u_Texture");
    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

我猜这是一个二次幂问题。

默认情况下，glTexParameter 的 GL_TEXTURE_WRAP 设置为 GL_REPEAT，并且使用 GL_REPEAT 的纹理<强>必须是二次方大小:

Similarly, if the width or height of a texture image are not powers of two and either the GL_TEXTURE_MIN_FILTER is set to one of the functions that requires mipmaps or the GL_TEXTURE_WRAP_S or GL_TEXTURE_WRAP_T is not set to GL_CLAMP_TO_EDGE, then the texture image unit will return (R, G, B, A) = (0, 0, 0, 1).

您可能会从 2 的幂纹理开始，但是当您使用 BitmapFactory.decodeResource 生成位图时，它会根据设备的密度有用地(？)缩放位图。因此，例如，如果您从 HDPI 设备上的 drawable 文件夹加载 512*512 源纹理，我相信它会将其缩放 1.5 倍，因此您留下的不是 Po2 的东西。

这会导致您的纹理无法在大量设备上工作，因为这些设备的密度都会导致您生成非法的纹理尺寸。

这种情况下的解决方案是将您的(2 的幂)源纹理放入资源文件夹 drawable-nodpi 中，这将防止任何基于密度的缩放。要么使用 CLAMP_TO_EDGE，后者不关心 Po2。