Android OpenGL着色器-以1：1大小显示图像

Question

Hi I have a 512x512 texture that I would like to display within my GlSurfaceview at a 100% scale at a 1:1 pixel for pixel view. I have having troubles achieving this and require some assistance. Every combination of settings in OnSurfaceChanged and onDrawFrame result in a scaled image. Can someone pls direct me to an example where this is possible.

private float[] mProjectionMatrix = new float[16];

// where mWidth and mHeight are set to 512
public void onSurfaceChanged(GL10 gl, int mWidth, int mHeight) {
 GLES20.glViewport(0, 0, mWidth, mHeight); 
 float left = -1.0f /(1/ScreenRatio );
 float right = 1.0f /(1/ScreenRatio );
 float bottom = -1.0f ;
 float top = 1.0f   ;
 final float near = 1.0f;
 final float far = 10.0f;
 Matrix.frustumM(mProjectionMatrix, 0, left, right, bottom, top, near, far);
}

@Override
public void onDrawFrame(GL10 glUnused ) {
 ....stuff here 
 Matrix.setIdentityM(mModelMatrix, 0); 
 Matrix.translateM(mModelMatrix, 0, 0, 0, 1);
 Matrix.rotateM(mModelMatrix, 0, 0.0f, 1.0f, 1.0f, 0.0f); 
 drawCube(); 
}  

many thanks,

Answer 1

There's various options. The simplest IMHO is to not apply any view/projection transformations at all. Then draw a textured quad with a range of (-1.0, 1.0) for both the x- and y-coordinates. That would get your texture to fill the entire view. Since you want it displayed in a 512x512 part of the view, you can set the viewport to cover only that area:

glViewport(0, 0, 512, 512);

Another possibility is that you reduce the range of your input coordinates to map to a 512x512 area of the screen. Or scale the coordinates in the vertex shader.

You didn't specify what version of OpenGL ES you use. In ES 3.0, you could also use glBlitFramebuffer() to copy the texture to your view.