Hi,

I came across a problem in Galaxy Tab 2 with Android 4.0.4 using Open GL ES 2: it does not draw correctly when using GL_POINTS or GL_LINES, only with GL_TRIANGLES*. The coordinates for the points and lines are computed incorrectly. For example, drawing a line at 0,10 to 0,20 draws nothing.

The code works fine on other Samsung and Sony devices, but fails on the Tab2.

To bypass the problem, when i want to draw a set of pixels, i'm drawing filled rectangles with width/height=1.
However, i'm hitting a performance problem: the performance is now 2x worst, since, for each pixel, i have to draw 4 vertices.

This is the code to draw a filled rectangle, and the code to draw the pixel:

Code :
#define LRP_VERTEX_CODE \
      "attribute vec4 a_Position;" \
      "uniform mat4 projectionMatrix;" \
      "void main() {gl_PointSize = 1.0; gl_Position = a_Position*projectionMatrix;}"
 
#define LRP_FRAGMENT_CODE \
      "precision mediump float;" \
      "uniform vec4 a_Color;" \
      "void main() {gl_FragColor = a_Color;}"
 
   lrpColor = glGetUniformLocation(lrpProgram, "a_Color");
   lrpPosition = glGetAttribLocation(lrpProgram, "a_Position"); // get handle to vertex shader's vPosition member
   glEnableVertexAttribArray(lrpPosition); // Enable a handle to the vertices - since this is the only one used, keep it enabled all the time
 
void glDrawPixel(int32 x, int32 y, int32 rgb)
{
   glFillRect(x,y,1,1,rgb);
}
 
void glFillRect(int32 x, int32 y, int32 w, int32 h, int32 rgb)
{
   GLfloat* coords = lrcoords;
   PixelConv pc;
   pc.pixel = rgb;
   coords[0] = coords[3]  = x;
   coords[1] = coords[10] = y;
   coords[4] = coords[7]  = y+h;
   coords[6] = coords[9]  = x+w;
 
   setCurrentProgram(lrpProgram);
   glUniform4f(lrpColor, f255[pc.r], f255[pc.g], f255[pc.b], 1);
   glVertexAttribPointer(lrpPosition, COORDS_PER_VERTEX, GL_FLOAT, GL_FALSE, COORDS_PER_VERTEX * sizeof(float), coords);
   glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, rectOrder);
}

Does anyone knows how can i optimize this situation? I tried to draw 1 triangle to draw the single point, but i'm unable to get it working. Any clues on this?

thanks

guich