How is this glowing with colors radiating outward 2D effect accomplished?

Question

I'm currently totally at a loss as to how this effect is done: http://www.youtube.com/watch?v=zp8MHUNp7Cg

The glowing on the ship and the changing color. I want to do this effect in XNA 4.0 any hints and tips?

Answer 1

It looks like simple vertex colouring where the colour index is function of the distance to the centre of the ship, plus time.

This can be implemented using a texture storing a palette. It could also be done proceduraly if the desired colour gradients are simple enough.

If using a palette, the vertex shader would be something like this:

uniform float4 in_ShipCenter; /* Centre of the ship */
uniform float in_Time;        /* Elapsed time */
/* ... */

void main(float4 in_Position : POSITION,
          uniform sampler1D in_Palette,
          /* ... */
          out float4 out_Color : COLOR)
{
    /* ... */
    float distance = length((in_Position - in_ShipCenter).xyz);
    float time = in_Time;

    /* Simple distance/time combination */
    vec2 colorIndex = vec2(distance + time, 0.5);

    /* Other possible effects:
     * vec2 colorIndex = vec2(A * distance + B * time, 0.5);
     * vec2 colorIndex = vec2(distance, time);
     * vec2 colorIndex = vec2(distance + A * time, time + B * distance); */

    /* Query the colour in the two-dimensional texture palette. */
    out_Color = tex2D(in_Palette, colorIndex);
}

Edit: account for the fact that XNA doesn't support 1D palettes. If you still want to access the pixels of a 2D palette as if it was a 1D palette, see this question.