Question

我正在尝试创建一个使用OpenGL显示文本的应用程序。当我尝试使用Matrix.translateM将指定对象移动到特定位置时，我会遇到意外行为。所有其他转换矩阵都像我期望的那样工作。

这是我打电话给Matrix.translateM(model_matrix, 0, -1.0f, 0, 0)时得到的： result image

这是没有翻译的图片： enter image description here

这是我的渲染器代码。

@Override
public void onSurfaceCreated(GL10 unused, EGLConfig config) {
    GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
    GLES20.glDisable(GLES20.GL_DEPTH_TEST);
    GLES20.glEnable(GLES20.GL_BLEND);
    GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);

    // create programs
    simple_texture = new SimpleTexture();

    // create shapes
    square = new Square();

    // create debug text handlers
    text_fps = new Text(this.font, this.text_scale);
    text_fps.setSize(50);
    text_fps.setText("Test\nLonger line");

    // set camera position
    final float eyeX = 0.0f;
    final float eyeY = 0.0f;
    final float eyeZ = -3.0f;

    final float lookX = 0.0f;
    final float lookY = 0.0f;
    final float lookZ = 0.0f;

    final float upX = 0.0f;
    final float upY = 1.0f;
    final float upZ = 0.0f;

    Matrix.setLookAtM(view_matrix, 0, eyeX, eyeY, eyeZ, lookX, lookY, lookZ, upX, upY, upZ);
}

@Override
public void onSurfaceChanged(GL10 unused, int width, int height) {
    GLES20.glViewport(0, 0, width, height);

    // set projection matrix
    float ratio = (float) width / height;
    Matrix.orthoM(projection_matrix, 0, -ratio, ratio, -1, 1, 3, 7);

    setScreenRatio(ratio);
    setScreenHeight(height);
}

@Override
public void onDrawFrame(GL10 unused) {
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);

    // calculate projection and view transformation
    Matrix.multiplyMM(vp_matrix, 0, projection_matrix, 0, view_matrix, 0);

    // if we are connected to debugger draw statistics
    drawStatistics(vp_matrix);
}

这是我的draw文字代码。

    // use predefined program
    GLES20.glUseProgram(program);

    // get attribute positions
    attr_matrix = GLES20.glGetUniformLocation(program, "u_Matrix");
    attr_position = GLES20.glGetAttribLocation(program, "a_Position");
    attr_texture_position = GLES20.glGetAttribLocation(program, "a_TexturePosition");
    attr_texture = GLES20.glGetUniformLocation(program, "u_Texture");

    // set program parameters
    GLES20.glEnableVertexAttribArray(attr_position);
    GLES20.glVertexAttribPointer(attr_position, 2, GLES20.GL_FLOAT, false, 2 * 4, square_buffer);

    // set texture parameters
    GLES20.glEnableVertexAttribArray(attr_texture_position);
    GLES20.glVertexAttribPointer(attr_texture_position, 2, GLES20.GL_FLOAT, false, 2 * 4, texture_buffer);

    // set matrix
    float[] result = new float[16];
    float ratio = (float) texture_height / texture_width;
    float screen_scale = (float) texture_height / PageRenderer.getScreenHeight();

    Matrix.setIdentityM(model_matrix, 0);
    Matrix.translateM(model_matrix, 0, -1, 0, 0);
    Matrix.scaleM(model_matrix, 0, screen_scale, screen_scale * ratio, screen_scale);

    Matrix.setIdentityM(result, 0);
    Matrix.multiplyMM(result, 0, matrix, 0, model_matrix, 0);
    GLES20.glUniformMatrix4fv(attr_matrix, 1, false, result, 0);

    // assign texture
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, index);
    GLES20.glUniform1i(attr_texture, 0);

    // perform drawing
    GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

    // disable vertex array
    GLES20.glDisableVertexAttribArray(attr_position);
    GLES20.glDisableVertexAttribArray(attr_texture_position);

着色器：

    int vertex_shader = PageRenderer.loadShader(
            GLES20.GL_VERTEX_SHADER, 
            "uniform mat4 u_Matrix;" + 
            "attribute vec4 a_Position;" +
            "attribute vec2 a_TexturePosition;" +
            "varying vec2 v_TexturePosition;" +
            "void main() {" + 
            "   gl_Position = a_Position * u_Matrix;" +
            "   v_TexturePosition = a_TexturePosition;" +
            "}"
        );
    int fragment_shader = PageRenderer.loadShader(
            GLES20.GL_FRAGMENT_SHADER, 
            "precision mediump float;" +
            "varying vec2 v_TexturePosition;" +
            "uniform sampler2D u_Texture;" +
            "void main() {" +
            "   gl_FragColor = texture2D(u_Texture, v_TexturePosition);" +
            "}"
        );

按预期缩放和旋转工作，但我无法弄清楚为什么翻译不会。请注意，我最近才使用OpenGL。

我希望translateM将文字移到左边，而不是“旋转”它。

Answer 1

计算gl_Position时的变量顺序很重要！世界矩阵首先是顶点坐标，然后是顶点坐标。在提问时我确实知道这一点，但由于着色器代码来自Android OpenGL教程，所以没有注意。是有趣的人。教程不正确！

更正着色器代码：

    int vertex_shader = PageRenderer.loadShader(
            GLES20.GL_VERTEX_SHADER, 
            "uniform mat4 u_Matrix;" + 
            "attribute vec4 a_Position;" +
            "attribute vec2 a_TexturePosition;" +
            "varying vec2 v_TexturePosition;" +
            "void main() {" + 
            "   gl_Position = u_Matrix * a_Position;" +
            "   v_TexturePosition = a_TexturePosition;" +
            "}"
        );
    int fragment_shader = PageRenderer.loadShader(
            GLES20.GL_FRAGMENT_SHADER, 
            "precision mediump float;" +
            "varying vec2 v_TexturePosition;" +
            "uniform sampler2D u_Texture;" +
            "void main() {" +
            "   gl_FragColor = texture2D(u_Texture, v_TexturePosition);" +
            "}"
        );

Android OpenGL ES 2.0：使用Matrix.traslateM无法获得我想要的结果

1 个答案: