LightningEffect
If the graphics implementation (i.e. Java2D, HTML5 Canvas, etc) doesn't support glows, you can add it as a post-processing step.
Here is how it would be achieved in GLSL:
GLSL Gaussian Blur
(Check out the GLSL tutorials if you're new to shaders)
Here is some very rough code for blurring in software (e.g. Java2D).
public static final float[] weights = new float[] { 0.05f, 0.09f, 0.12f, 0.15f, 0.16f, 0.15f, 0.12f, 0.09f, 0.05f }; void blur(byte[] px, byte[] out) { //assuming type 4BYTE_ARGB //value between 0 and 255 to increase final output brightness final int brightness = 0; //horizontal blur for (int j=0; j<WIDTH*HEIGHT*4; j+=4) { final int y = j/4 / WIDTH; final int x = j/4 - WIDTH*y; //this code only blurs the R channel, e.g. for grayscale alpha images //for RGBA you would need sumR, sumG, sumB int sumL = 0; int sumA = 0; for (int off=-4, idx=0; off<=4; off++, idx++) { int pxOff = off; if (x+pxOff < 0 || x+pxOff >= WIDTH) pxOff = 0; //CLAMP_TO_EDGE sumL += (buffer[j + pxOff*4 + 1] & 0xFF) * weights[idx]; sumA += (buffer[j + pxOff*4 + 0] & 0xFF) * weights[idx] + 0.5f; //HACK: adding 0.5 to alpha fixes some transparency loss } byte sumLB = (byte)Math.max(0, Math.min(255, sumL)); buffer[j+1] = buffer[j+2] = buffer[j+3] = sumLB; //alpha buffer[j] = (byte)Math.max(0, Math.min(255, sumA)); } //vertical blur for (int j=0; j<WIDTH*HEIGHT*4; j+=4) { final int y = j/4 / WIDTH; final int x = j/4 - WIDTH*y; int sumL = 0; int sumA = 0; for (int off=-4, idx=0; off<=4; off++, idx++) { int pxOff = off; if (y+pxOff < 0 || y+pxOff >= HEIGHT) pxOff = 0; //CLAMP_TO_EDGE pxOff *= WIDTH; sumL += (buffer[j + pxOff*4 + 1] & 0xFF) * weights[idx]; sumA += (buffer[j + pxOff*4 + 0] & 0xFF) * weights[idx] + 0.5f; //HACK: adding 0.5 to alpha fixes some transparency loss } out[j+1] = out[j+2] = out[j+3] = (byte)Math.max(0, Math.min(255, sumL+brightness)); out[j+0] = (byte)Math.max(0, Math.min(255, sumA)); } }