android res trick

package prod.demo.intro;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.content.Context;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;
import android.os.SystemClock;
import android.util.Log;
class IntroRenderer implements GLSurfaceView.Renderer {
  private float[] v = {
    -1.0f,-1.0f,
    -1.0f,1.0f,
    1.0f,1.0f,
    -1.0f,-1.0f,
    1.0f,1.0f,
    1.0f,-1.0f
  };
  private float[] uv = {
    -1.0f,-1.0f,
    -1.0f,1.0f,
    1.0f,1.0f,
    -1.0f,-1.0f,
    1.0f,1.0f,
    1.0f,-1.0f
  };
  private FloatBuffer vbuf;
  private FloatBuffer uvbuf;
  private int fb[] = new int[1];
  private int drb[] = new int[1];
  private int tex[] = new int[1];
  private final String vs =
    "attribute vec4 apos;\n"+
      "attribute vec2 atex;\n"+
      "varying vec2 vtex;\n"+
      "void main() {\n"+
      "  gl_Position = apos;\n"+
      "  vtex = atex;\n"+
      "}\n";
  private final String fs =
    "precision mediump float;\n"+
      "varying vec2 vtex;\n"+
      "void main() {\n"+
      "  gl_FragColor = vec4(abs(vtex.x),abs(vtex.y),0.0,1.0);\n"+
      "}\n";
  private final String texvs =
    "attribute vec4 aPosition;\n"+
      "attribute vec2 aTextureCoord;\n"+
      "varying vec2 vTextureCoord;\n"+
      "void main() {\n"+
      "  gl_Position = aPosition;\n"+
      "  vTextureCoord = aTextureCoord;\n"+
      "}\n";
  private final String texfs =
    "precision mediump float;\n"+
      "varying vec2 vTextureCoord;\n"+
      "uniform sampler2D sTexture;\n"+
      "void main() {\n"+
      "  gl_FragColor = texture2D(sTexture, vTextureCoord);\n"+
      "}\n";
  private int prog, texprog;
  private static String TAG = "GLES20TriangleRenderer";
  public IntroRenderer(Context context) {
    vbuf = ByteBuffer.allocateDirect(v.length*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
    vbuf.put(v).position(0);
    uvbuf = ByteBuffer.allocateDirect(uv.length*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
    uvbuf.put(uv).position(0);
  }
  static long lastTime = SystemClock.uptimeMillis();
  static long frameCount = 0;
  int texresx, texresy;
  IntBuffer texbuf;
  private void generateTexture() {
    GLES20.glGenFramebuffers(1,fb,0);
    GLES20.glGenRenderbuffers(1,drb,0);
    GLES20.glGenTextures(1,tex,0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D,tex[0]);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D,GLES20.GL_TEXTURE_WRAP_S,GLES20.GL_CLAMP_TO_EDGE);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D,GLES20.GL_TEXTURE_WRAP_T,GLES20.GL_CLAMP_TO_EDGE);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D,GLES20.GL_TEXTURE_MAG_FILTER,GLES20.GL_NEAREST);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D,GLES20.GL_TEXTURE_MIN_FILTER,GLES20.GL_NEAREST);
    int[] buf = new int[texresx*texresy];
    texbuf = ByteBuffer.allocateDirect(buf.length*4).order(ByteOrder.nativeOrder()).asIntBuffer();
    GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D,0,GLES20.GL_RGB,texresx,texresy,0,GLES20.GL_RGB,GLES20.GL_UNSIGNED_SHORT_5_6_5,texbuf);
    GLES20.glBindRenderbuffer(GLES20.GL_RENDERBUFFER,drb[0]);
    GLES20.glRenderbufferStorage(GLES20.GL_RENDERBUFFER,GLES20.GL_DEPTH_COMPONENT16,texresx,texresy);
  }
  public void onDrawFrame(GL10 glUnused) {
    frameCount++;
    long time = SystemClock.uptimeMillis();
    if(time>lastTime+1000) {
      System.out.println("fps: "+frameCount);
      frameCount = 0;
      lastTime = time;
    }
    // setup render to texture
    // GLES20.glViewport(0,0,texresx,texresy);
    // GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER,fb[0]);
    // GLES20.glFramebufferTexture2D(GLES20.GL_FRAMEBUFFER,GLES20.GL_COLOR_ATTACHMENT0,GLES20.GL_TEXTURE_2D,tex[0],0);
    // GLES20.glFramebufferRenderbuffer(GLES20.GL_FRAMEBUFFER,GLES20.GL_DEPTH_ATTACHMENT,GLES20.GL_RENDERBUFFER,drb[0]);
    // render shader
    GLES20.glViewport(0,0,xres,yres);
    GLES20.glUseProgram(prog);
    GLES20.glClearColor(0.0f,0.0f,0.0f,1.0f);
    GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT|GLES20.GL_COLOR_BUFFER_BIT);
    GLES20.glVertexAttribPointer(GLES20.glGetAttribLocation(prog,"apos"),2,GLES20.GL_FLOAT,false,2*4,vbuf);
    GLES20.glEnableVertexAttribArray(GLES20.glGetAttribLocation(prog,"apos"));
    GLES20.glVertexAttribPointer(GLES20.glGetAttribLocation(prog,"atex"),2,GLES20.GL_FLOAT,false,2*4,uvbuf);
    GLES20.glEnableVertexAttribArray(GLES20.glGetAttribLocation(prog,"atex"));
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES,0,v.length/2);
    // render texture
    // GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER,0);
    // GLES20.glViewport(0,0,xres,yres);
    // GLES20.glUseProgram(texprog);
    // GLES20.glClearColor(0.0f,0.0f,0.0f,1.0f);
    // GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT|GLES20.GL_COLOR_BUFFER_BIT);
    // send vertex coords
    // GLES20.glVertexAttribPointer(GLES20.glGetAttribLocation(texprog,"aPositionCoord"),2,GLES20.GL_FLOAT,false,2*4,vbuf);
    // GLES20.glEnableVertexAttribArray(GLES20.glGetAttribLocation(texprog,"aPositionCoord"));
    // bind framebuffer texture
    // GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    // GLES20.glBindTexture(GLES20.GL_TEXTURE_2D,tex[0]);
    // GLES20.glUniform1i(GLES20.glGetUniformLocation(texprog,"texture1"),0);
    // GLES20.glUniform1f(GLES20.glGetUniformLocation(texprog,"hasTexture"),1.0f);
    // GLES20.glVertexAttribPointer(GLES20.glGetAttribLocation(texprog,"aTextureCoord"),2,GLES20.GL_FLOAT,false,2*4,uvbuf);
    // GLES20.glEnableVertexAttribArray(GLES20.glGetAttribLocation(texprog,"aTextureCoord"));
    // GLES20.glDrawArrays(GLES20.GL_TRIANGLES,0,v.length/2);
  }
  private int xres, yres;
  public void onSurfaceChanged(GL10 glUnused, int width, int height) {
    GLES20.glViewport(0,0,width,height);
    xres = width;
    yres = height;
    float ratio = (float)width/height;
    // float tempuv[] = {
    // -ratio,-1.0f,
    // -ratio,1.0f,
    // ratio,1.0f,
    // -ratio,-1.0f,
    // ratio,1.0f,
    // ratio,-1.0f
    // };
    float tempuv[] = {
      -1.0f,-1.0f,
      -1.0f,1.0f,
      1.0f,1.0f,
      -1.0f,-1.0f,
      1.0f,1.0f,
      1.0f,-1.0f
    };
    uv = tempuv;
    uvbuf = ByteBuffer.allocateDirect(uv.length*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
    uvbuf.put(uv).position(0);
    texresx = xres/64;
    texresy = yres/64;
    generateTexture();
  }
  public void onSurfaceCreated(GL10 glUnused, EGLConfig config) {
    prog = createProgram(vs,fs);
    texprog = createProgram(texvs,texfs);
  }
  private int loadShader(int shaderType, String source) {
    int shader = GLES20.glCreateShader(shaderType);
    if(shader!=0) {
      GLES20.glShaderSource(shader,source);
      GLES20.glCompileShader(shader);
      int[] compiled = new int[1];
      GLES20.glGetShaderiv(shader,GLES20.GL_COMPILE_STATUS,compiled,0);
      if(compiled[0]==0) {
        Log.e(TAG,"Could not compile shader "+shaderType+":");
        Log.e(TAG,GLES20.glGetShaderInfoLog(shader));
        GLES20.glDeleteShader(shader);
        shader = 0;
      }
    }
    return shader;
  }
  private int createProgram(String vertexSource, String fragmentSource) {
    int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER,vertexSource);
    if(vertexShader==0) {
      return 0;
    }
    int pixelShader = loadShader(GLES20.GL_FRAGMENT_SHADER,fragmentSource);
    if(pixelShader==0) {
      return 0;
    }
    int program = GLES20.glCreateProgram();
    if(program!=0) {
      GLES20.glAttachShader(program,vertexShader);
      checkGlError("glAttachShader");
      GLES20.glAttachShader(program,pixelShader);
      checkGlError("glAttachShader");
      GLES20.glLinkProgram(program);
      int[] linkStatus = new int[1];
      GLES20.glGetProgramiv(program,GLES20.GL_LINK_STATUS,linkStatus,0);
      if(linkStatus[0]!=GLES20.GL_TRUE) {
        Log.e(TAG,"Could not link program: ");
        Log.e(TAG,GLES20.glGetProgramInfoLog(program));
        GLES20.glDeleteProgram(program);
        program = 0;
      }
    }
    return program;
  }
  private void checkGlError(String op) {
    int error;
    while ((error = GLES20.glGetError())!=GLES20.GL_NO_ERROR) {
      Log.e(TAG,op+": glError "+error);
      throw new RuntimeException(op+": glError "+error);
    }
  }
}