ES 2.0 Fundamentals - Learn OpenGL ES: For Mobile Game and Graphics Development - page 106

Using glDrawArrays , with mode GL_TRIANGLES , an easy way to render a
rectangle is by creating a float array for points that form a closed loop. When we
call glDrawArrays for such a collection of points, we need to pass the count ar-
gument as '6.' The float array given in Listing 3-23 is a collection of three points
for each of the upper and lower triangles.

Listing 3-23. GL RECTANGLE/src/com/apress/android/glrectangle/

GLES20Renderer.java

float rectangleVFA[] = {
0, 0, 0,
0, 0.5f, 0,
0.75f, 0.5f, 0, // upper triangle
0.75f, 0.5f, 0,
0.75f, 0, 0,
0, 0, 0, // lower triangle

};

You must make three changes to the GL POINT ADVANCED application to render a
rectangle as shown in Figure 3-14 :

1. Remove the line “ gl_PointSize = 15.0; \n ” from the point
vertex shader code ( _pointVertexShaderCode ).

2. Replace the contents of array pointVFA (inside initShapes meth-
od) with the points given in Listing 3-23 .
3. Modify the call to GLES20.glDrawArrays method as
GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 6); .