I am trying to implement a simple heightmap editor. In this editor, you can elevate the terrain by clicking on a spot in the heightmap, and holding down the mouse button. This will little by little, every frame, elevate the terrain into a hillshape. The hills created looks like this:


As can be observed, however, the edges of the hill has some pretty awful jagged edges:


I am not quite sure how to get rid of these edges. For every frame that I hold down the mouse, the following code is executed:

float rad = 35;
for(int ix = -rad; ix <= +rad; ++ix) {

    for(int iz = -rad; iz <= +rad; ++iz) {

    // distance from center of hill.
    float dist = sqrt( (float)ix * (float)ix + (float)iz * (float)iz  );

    // if within the radius of the hill(this ensures that the hill is round)
    if(dist <= rad) {

        // the farther we get from the center, the less we increase the height.
        // this effectively results in a radial gradient being added to the
        // heightmap.
        // Note that we use "x*x" instead of "x", because this results in a
        // more round and natural-looking hill
        float x = dist / rad;
        float y = (1.0 - x*x);

        // maximum height of the hill
        float maxHeight =y * (float)MAX_HEIGHT;

          Note that cx and cz describe the center position of the hill.

        if( heightData(cx+ix,cz+iz) < (float)MAX_HEIGHT) { // do not exceed the maximum height

             // if we hold down the mouse for 30 frames, the hill will reach its maximum height
             float increment = maxHeight  / 30.0;

            if(heightData(cx+ix,cz+iz) + increment > MAX_HEIGHT) {
                 // clamp the hill height so that it does not exceed the maximum height of the
                // height map.
                heightData(cx+ix,cz+iz) = MAX_HEIGHT;
            } else {
            heightData(cx+ix,cz+iz) += increment;


    } // end for
} // end for

As can be observed, every frame I simply add a radial gradient to the heightmap. MAX_HEIGHT = 65535;, because the heightmap is a grid of unsigned shorts. And the resolution of the heightmap is 256x256. But even if I increased it to 512x512, the jaggies still remained.


The root cause of your artifact is likely the harsh cutoff at rad. As you accumulate elevation, the boundary gets very discontinuous.

As for solutions, I would recommend a slightly wider filter that tends toward zero outside the desired action radius, or shrink the current filter to avoid missing grid cells that are at the boundary.

  • \$\begingroup\$ Yes, if I start interpolating towards zero near the radius, the problem is solved. If, in the original code, after the line float y = (1.0 - x*x); I add if(dist > fade_rad) { y *= (1.0f- (dist - fade_rad ) / (rad-fade_rad) ); }, then it looks much better. Where fade_rad=30, and it is the radius at which we start interpolating. Thanks for the help! \$\endgroup\$ – Erkaman Dec 28 '15 at 11:04

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