OpenGL ES球体上的照明不平滑

Question

In OpenGL ES 2.0 for Android, I am drawing a sphere. The sphere appears on the screen as a circle, so I need to add lighting. When I added lighting, instead of it being smooth, like it would be in real life, it is a fine line between light and dark, as shown here:

However, I want it to look like this, where the shading is much smoother and blended:

Here is my vertex shader code:

uniform mat4 u_Matrix;
uniform vec3 u_VectorToLight;

attribute vec4 a_Position;
attribute vec3 a_Color;
attribute vec3 a_Normal;

varying vec3 v_Color;

void main() {
  v_Color = a_Color;
  vec3 scaledNormal = a_Normal;
  scaledNormal = normalize(scaledNormal);
  float diffuse = max(dot(scaledNormal, u_VectorToLight), 0.0);
  v_Color *= diffuse;
  float ambient = 0.1;
  v_Color += ambient;
  gl_Position = u_Matrix * a_Position;
}

And my fragment shader:

precision mediump float;

varying vec3 v_Color;

void main() {
  gl_FragColor = vec4(v_Color, 1.0);
}

The normal is calculated by getting the vector from the center of the sphere to the point on the sphere, then normalizing it (giving it a length of 1)

Here is how I set the colors:

vertices[offset++] = Color.red(color);
vertices[offset++] = Color.green(color);
vertices[offset++] = Color.blue(color);

Where color is 0xffea00.

Answer 1

The problem is with the range of color values you use. OpenGL operates with color component values in the range [0.0, 1.0]. But you are specifying colors in the range [0, 255] in your Java code.

You have two options to fix this:

• Divide the color values you get from the Color class by 255.0f.

• Specify the colors with type GL_UNSIGNED_BYTE . To do this, store the values in an array/buffer with element type byte , store those values in a VBO, and then set up the vertex attribute with:

   glVertexAttribPointer(attrLoc, 3, GL_UNSIGNED_BYTE, GL_TRUE, stride, 0); 

  Note the value for the 4th argument. While it does not matter for GL_FLOAT attributes, it is critical that you use GL_TRUE in this case, because the byte values need to be normalized.