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,我得到了意外的行为.所有其他转换矩阵都像我期望的那样工作.
这是我调用Matrix.translateM(model_matrix,-1.0f,0)时得到的结果:
这是没有翻译的图片:
这是我的渲染器代码.
@Override public void onSurfaceCreated(GL10 unused,EGLConfig config) { GLES20.glClearColor(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,eyeX,eyeY,eyeZ,lookX,lookY,lookZ,upX,upY,upZ); } @Override public void onSurfaceChanged(GL10 unused,int width,int height) { GLES20.glViewport(0,width,height); // set projection matrix float ratio = (float) width / height; Matrix.orthoM(projection_matrix,-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,projection_matrix,view_matrix,0); // if we are connected to debugger draw statistics drawStatistics(vp_matrix); }
// 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,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); Matrix.scaleM(model_matrix,screen_scale,screen_scale * ratio,screen_scale); Matrix.setIdentityM(result,0); Matrix.multiplyMM(result,matrix,model_matrix,0); GLES20.glUniformMatrix4fv(attr_matrix,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,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.
我期待translateM将文本移动到左侧,而不是“旋转”它.
解决方法
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,v_TexturePosition);" + "}" );