ES 2.0 Fundamentals - Learn OpenGL ES: For Mobile Game and Graphics Development - page 104

GLES20.glVertexAttribPointer(_lineAColorLocation, 4,
GLES20.GL_FLOAT, false, 0, _lineCFB);
GLES20.glEnableVertexAttribArray(_lineAColorLocation);
GLES20.glLineWidth(3);
GLES20.glDrawArrays(GLES20.GL_LINES, 0, 2);
}
Next, take a look at the vertex and fragment shaders ( Listing 3-22 ). Notice how the
varying variable vColor is shared by each of these shaders. As previously men-
tioned, its type should match in both the shaders.
Inside the vertex shader, vColor receives per-vertex color data (blue and yellow
color) from the attribute variable aColor . When the rendering pipeline processes
the fragments using fragment shader, it interpolates this per-vertex data across the
primitive (that is, across the fragments occupied by the primitive). This is why blue
color at one endpoint of the line primitive interpolates to yellow color at the other
( Figure 3-12 ).
Listing 3-22. GL VARYING/src/com/apress/android/glvarying/GLES20Render-
er.java
private final String _lineVertexShaderCode =
"attribute vec4 aPosition;"
+ "attribute vec4 aColor;"
+ "varying vec4 vColor;"
+ "void main() {"
+ " vColor = aColor;"
+ " gl_Position = aPosition;"
+ "}";
private final String _lineFragmentShaderCode =
"#ifdef GL_FRAGMENT_PRECISION_HIGH \n"
+ "precision highp float;"
+ "#else \n"
+ "precision mediump float;"
+ "#endif \n"
+ "varying vec4 vColor;"
+ "void main() {"
+ " gl_FragColor = vColor;"