Reusable 3D Earth globe widget (pure OCaml + WebGL)
feat(ocaml-globe): dim Earth when coverage is active, spotlight effect
Earth.draw now takes ?dim parameter (0.0–1.0) to control base
brightness. When orbits+coverage are shown, Earth renders at ~20-25%
brightness. Coverage additive blending then lights up the areas under
satellite footprints back to full brightness — only visible parts of
the Earth glow, everything else stays dark.
The visual flow:
1. Dim Earth dots (u_dim uniform in fragment shader)
2. Grid overlay (unaffected)
3. Coverage filled triangles (additive blend brightens underlying dots)
4. Net result: dark globe with bright spotlights under each satellite
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demo/main.ml
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demo/main.ml
···
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Globe_webgl.Stars.draw gl stars ~projection ~view;
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Gl.enable gl Gl.depth_test
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end;
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if Signal.get show_dots then
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Globe_webgl.Earth.draw gl earth ~projection ~view;
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if Signal.get show_dots then begin
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let dim =
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if Signal.get show_coverage && Signal.get show_orbits then 0.2
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else 1.0
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in
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Globe_webgl.Earth.draw gl earth ~projection ~view ~dim ()
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end;
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if Signal.get show_grid then
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Globe_webgl.Grid.draw gl !grid ~projection ~view
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~color:(0.1, 0.3, 0.5) ~alpha:0.25 ();
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webgl/earth.ml
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webgl/earth.ml
···
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u_projection : Gl.uniform_location;
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u_view : Gl.uniform_location;
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u_point_size : Gl.uniform_location;
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u_dim : Gl.uniform_location;
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}
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let v ?(num_points = 30000) gl =
···
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Gl.enable_vertex_attrib_array gl 1;
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Gl.vertex_attrib_pointer gl 1 1 Gl.float false 16 12;
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Gl.bind_vertex_array gl None;
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let u name = Gl.get_uniform_location gl prog (Jstr.of_string name) in
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{
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prog;
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vao;
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num_points = n;
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u_projection =
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Gl.get_uniform_location gl prog (Jstr.of_string "u_projection");
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u_view = Gl.get_uniform_location gl prog (Jstr.of_string "u_view");
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u_point_size =
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Gl.get_uniform_location gl prog (Jstr.of_string "u_point_size");
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u_projection = u "u_projection";
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u_view = u "u_view";
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u_point_size = u "u_point_size";
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u_dim = u "u_dim";
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}
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let draw gl t ~projection ~view =
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let draw gl t ~projection ~view ?(dim = 1.0) () =
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Gl.use_program gl t.prog;
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let proj_arr = Tarray.of_float_array Tarray.Float32 projection in
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let view_arr = Tarray.of_float_array Tarray.Float32 view in
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Gl.uniform_matrix4fv gl t.u_projection false proj_arr;
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Gl.uniform_matrix4fv gl t.u_view false view_arr;
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Gl.uniform_matrix4fv gl t.u_projection false
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(Tarray.of_float_array Tarray.Float32 projection);
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Gl.uniform_matrix4fv gl t.u_view false
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(Tarray.of_float_array Tarray.Float32 view);
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Gl.uniform1f gl t.u_point_size 3.5;
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Gl.uniform1f gl t.u_dim dim;
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Gl.bind_vertex_array gl (Some t.vao);
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Gl.draw_arrays gl Gl.points 0 t.num_points;
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Gl.bind_vertex_array gl None
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webgl/earth.mli
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webgl/earth.mli
···
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(default 30000). *)
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val draw :
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Brr_canvas.Gl.t -> t -> projection:float array -> view:float array -> unit
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(** [draw gl t ~projection ~view] renders the Earth dot cloud. *)
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Brr_canvas.Gl.t ->
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t ->
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projection:float array ->
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view:float array ->
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?dim:float ->
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unit ->
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unit
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(** [draw gl t ~projection ~view ?dim ()] renders the Earth dot cloud.
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[dim] (default 1.0) controls overall brightness: 1.0 = full,
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0.0 = invisible. Use ~0.25 when coverage is shown so that only
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areas under satellite footprints appear bright via additive blending. *)
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webgl/shader.ml
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webgl/shader.ml
···
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precision highp float;
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in float v_brightness;
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uniform float u_dim;
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out vec4 fragColor;
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void main() {
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float d = distance(gl_PointCoord, vec2(0.5));
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if (d > 0.5) discard;
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float alpha = smoothstep(0.5, 0.1, d);
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// Dark ocean blue → bright cyan coastline
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vec3 color = mix(vec3(0.03, 0.10, 0.25), vec3(0.35, 0.90, 1.0), v_brightness);
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fragColor = vec4(color, alpha * (0.3 + v_brightness * 0.7));
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// u_dim: 1.0 = full brightness, 0.0 = completely dark
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fragColor = vec4(color * u_dim, alpha * (0.3 + v_brightness * 0.7) * u_dim);
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}
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|}
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