GL_POINTS not drawing points in Android

Hi,

I posted this on android forum but i’m sure that this forum is a better place to post this question.

I’ve spent a full day trying to draw a series of points using GL_POINTS. I know i could use a texture, but i want to learn how to draw points. The resulting image (zoomed) is shown here:

The code is written below. Any help on why are only 4 points appearing is greatly appreciated. I also tried to print just 2 points, one at the site of the other, but they dont work.


public class MainActivity extends Activity
{
   class MyGLSurfaceView extends GLSurfaceView
   {
      public MyGLSurfaceView(Context context)
      {
         super(context);
        
         setEGLContextClientVersion(2); // Create an OpenGL ES 2.0 context.
         setEGLConfigChooser(8, 8, 8, 8, 0, 0);
         getHolder().setFormat(PixelFormat.RGBA_8888);
         setRenderer(new MyGLRenderer()); // Set the Renderer for drawing on the GLSurfaceView
//         setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY); // Render the view only when there is a change in the drawing data (must be after setRenderer!)
      }
   }

   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       setContentView(new MyGLSurfaceView(this));
   }  
}

class MyGLRenderer implements GLSurfaceView.Renderer
{
   byte[][] bitmap = {
         {1,1,1,1,1,1,1,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,0,0,1,1,0,0,1},
         {1,1,1,1,1,1,1,1}};
  
   static final int COORDS_PER_VERTEX = 3;

   // Set color with red, green, blue and alpha (opacity) values
   float color[] = { 0,0,0, 1.0f };
   float coords[] = new float[4 * COORDS_PER_VERTEX];
   int w,h;

   public void onSurfaceCreated(GL10 unused, EGLConfig config)
   {
   }

   public void onDrawFrame(GL10 unused)
   {
      try
      {
         drawText();
      } catch (Exception e) {debug(e.getMessage());}
   }

   private String vertexShaderCode(int w, int h)
   {
      return // http://www.songho.ca/opengl/gl_projectionmatrix.html
         "attribute vec4 vPosition;" +
         "mat4 projectionMatrix = mat4( 2.0/"+w+".0, 0.0, 0.0, -1.0,"+
                              "0.0, -2.0/"+h+".0, 0.0, 1.0,"+
                              "0.0, 0.0, -1.0, 0.0,"+
                              "0.0, 0.0, 0.0, 1.0);"+
         "void main() {gl_Position = vPosition*projectionMatrix;}"; // the matrix must be included as a modifier of gl_Position
   }

   private final String fragmentShaderCode =
      "precision mediump float;" +
      "uniform vec4 vColor;" +
      "void main() {gl_FragColor = vColor;}";

   private int mProgram;
   private int mPositionHandle;
   private int mColorHandle;

   public void onSurfaceChanged(GL10 unused, int width, int height)
   {
      w = width; h = height;
      // Adjust the viewport based on geometry changes, such as screen rotation
      GLES20.glViewport(0, 0, width, height);

      // prepare shaders and OpenGL program
      int vertexShader = MyGLRenderer.loadShader(GLES20.GL_VERTEX_SHADER,vertexShaderCode(width,height));
      int fragmentShader = MyGLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,fragmentShaderCode);

      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
      GLES20.glUseProgram(mProgram); // Add program to OpenGL environment

      // get handle to fragment shader's vColor member
      mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");
      mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition"); // get handle to vertex shader's vPosition member
      GLES20.glEnableVertexAttribArray(mPositionHandle); // Enable a handle to the vertices - since this is the only one used, keep it enabled all the time
   }

   float[] letter; int nletter;
   private FloatBuffer letBuffer;
   private void drawText()
   {
      setColor(0xFF00FFFF);
      if (letter == null)
      {
         letter = new float[200];
         for (int i = 0; i < bitmap.length; i++)
         {
            byte[]b = bitmap[i];
            for (int j = 0; j < b.length; j++)
               if (b[j] == 1)
               {
                  letter[nletter++] = j;
                  letter[nletter++] = i;
                  nletter++;
               }
         }
         ByteBuffer bb = ByteBuffer.allocateDirect(nletter * 4); // (# of coordinate values * 4 bytes per float)
         bb.order(ByteOrder.nativeOrder());
         letBuffer = bb.asFloatBuffer();
         letBuffer.put(letter,0,nletter); letBuffer.position(0);
      }
     
         int nn = nletter/3;
         GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT,
               false, COORDS_PER_VERTEX * nn, letBuffer);
         GLES20.glDrawArrays(GLES20.GL_POINTS, 0,nn);
   }

   public static int loadShader(int type, String shaderCode)
   {
      int shader = GLES20.glCreateShader(type);
      GLES20.glShaderSource(shader, shaderCode);
      GLES20.glCompileShader(shader);
      return shader;
   }

   public void setColor(int rgb)
   {
      color[0] = (float)((rgb >> 16 ) & 0xFF) / 255f;
      color[1] = (float)((rgb >> 8  ) & 0xFF) / 255f;
      color[2] = (float)((rgb       ) & 0xFF) / 255f;
      color[3] = (float)((rgb >>> 24) & 0xFF) / 255f;
      GLES20.glUniform4fv(mColorHandle, 1, color, 0); // Set color for drawing the line
   }
}

thanks,

guich

Check your stride argument to glVertexAttribPointer() call. Stride “specifies the byte offset between consecutive generic vertex attributes”.

Hi,

It doesnt work. In the more simple code below:


   final int COORDS_PER_VERTEX = 3;
   float[] letter; int nletter;
   private FloatBuffer letBuffer;
   private void drawText()
   {
      setColor(0xFF00FFFF);
      letter = new float[200];
      nletter = 0;
      for (int i =0; i < 10; i++)
      {
         letter[nletter++] = i+10;
         letter[nletter++] = 10;
         letter[nletter++] = 0;
      }
      
      ByteBuffer bb = ByteBuffer.allocateDirect(nletter * 4); // (# of coordinate values * 4 bytes per float)
      bb.order(ByteOrder.nativeOrder());
      letBuffer = bb.asFloatBuffer();
      letBuffer.put(letter,0,nletter); 
      letBuffer.position(0);
     
      int nn = nletter/3;
      int stride = COORDS_PER_VERTEX*nn;
      GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, stride, letBuffer);
      GLES20.glDrawArrays(GLES20.GL_POINTS, 0,nn);
   }

I already tried several options for stride, with no success.

thx

guich

Hi,

That was the problem. Using 12 (as each coordinate has 3 floats * 4 bytes per float) it works!

thanks!!!

I tried your code, and putting ‘12’ in various places, but to no avail.