WaterMars with Shader in Processing / Water Mars

_ WaterMars with Shader in Processing Water Mars.pde

PShader shader;
PImage colormap, heightmap, palette;
PShape shape;

void setup() {
  size(1169, 1169, P3D);
  shader = loadShader("watermars.glsl");
  colormap = loadImage("mars-2k-noaa.jpg");
  heightmap = loadImage("mars-4k-bump.png");
  palette = loadImage("water.png");

  sphereDetail(100);
  fill(255);
  shape = createShape(SPHERE, 500);
  shape.setStroke(false);
  
  shader.set("colormap",colormap);
  shader.set("heightmap",heightmap);
  shader.set("palette",palette);
}

void draw() {
  ortho();
  camera();
  translate(width/2,height/2);
  shader.set("progress",map(mouseX,0,width,0,1));
  shader(shader);
  shape(shape);
}

shader.glsl

uniform sampler2D colormap;
uniform sampler2D heightmap;
uniform sampler2D palette;
uniform sampler2D normalmap;
uniform sampler2D borders;
// uniform sampler2D overlay;
uniform float progress;
varying vec4 vertTexCoord;
const float fade =  0.001; //25;

float map(float value, float min1, float max1, float min2, float max2) {
  return min2 + (value - min1) * (max2 - min2) / (max1 - min1);
}

void main() {
  vec4 terrainColor = texture2D(colormap, vertTexCoord.st);
  vec4 heightColor = texture2D(heightmap, vertTexCoord.st);
  // vec4 overlayColor = texture2D(overlay, vertTexCoord.st);
  float elevation = (heightColor.r*256 + heightColor.g) / 256; //0..1
  vec4 waterColor = texture2D(palette, vec2(map(elevation,0,progress,0,.85),0));
  vec4 landColor = terrainColor;
  float d = smoothstep(progress-fade, progress+fade, elevation);
  vec4 color = mix(waterColor, landColor, d);

  // grid
  float gridResolution = .083333;
  float gridLineWidth = 1;
  vec2 distanceToLine = mod(vertTexCoord.st,gridResolution);
  vec2 dx = abs(dFdx(vertTexCoord.st));
  vec2 dy = abs(dFdy(vertTexCoord.st));
  vec2 dF = vec2(max(dx.s, dy.s), max(dx.t, dy.t)) * gridLineWidth;
  if (distanceToLine.x < dF.x || distanceToLine.y < dF.y) {
    float a = .1;
    color += vec4(a,a,a,0); //grid
  }

  // color = mix(color,overlayColor,overlayColor.a); //overlay

  gl_FragColor = color;
}

heightmap: https://globe4d.com/maps/mars-4k-bump.png