Custom Raster Shaders

CustomRasterTileLayer runs a custom GLSL "filter" shader over any raster tile source. It is the general base class that HillshadeRasterTileLayer specializes.

Fork feature

Added in PR #18.

What it does

The layer draws a raster source through a fragment shader you supply. Inside the shader you can:

• read the source pixel with getRawColor(),
• read the current zoom with getMapZoom(),
• return a premultiplied color.

This lets you recolor, threshold, blend or otherwise post-process any raster source on the GPU, per frame, with no CPU re-decode.

Usage

import com.massifmaps.layers.CustomRasterTileLayer
import com.massifmaps.datasources.HTTPTileDataSource

val source = HTTPTileDataSource(0, 19, "https://your.tiles/{z}/{x}/{y}.png")
val layer = CustomRasterTileLayer(source)

layer.setShaderSource("""
    // GLSL fragment "filter". Return a premultiplied vec4.
    vec4 filterColor() {
        vec4 c = getRawColor();
        float g = dot(c.rgb, vec3(0.299, 0.587, 0.114)); // grayscale
        return vec4(vec3(g) * c.a, c.a);
    }
""".trimIndent())

mapView.layers.add(layer)

With the surface API

There is no {"type": "custom-raster"} — the layer carries no !spec declaration. Construct it and adopt it; shaderSource is an ordinary property afterwards, so the shader can be swapped at runtime by one write:

MassifLayer tinted = Massif.adopt("tinted", new CustomRasterTileLayer(source));
tinted.set("shaderSource", grayscaleFilter);

shaderSource is also inherited by the hillshade layer, which does have a spec — so a shaded-relief layer with a custom filter needs no adoption at all.

Member	Purpose
setShaderSource(String)	Install the GLSL filter shader.
getShaderSource()	The shader you set.
getEffectiveShaderSource()	The full shader actually compiled (with SDK boilerplate).
getRawColor() (in shader)	The source pixel.
getMapZoom() (in shader)	Current map zoom, for zoom-dependent effects.

Relationship to hillshade

HillshadeRasterTileLayer is a CustomRasterTileLayer whose shader is the DEM lighting shader. Its virtual overrides shadow the base behavior, so hillshade works exactly as before — but you can build your own DEM-driven effects (per-zoom contours, custom relief, slope shading) by combining a custom shader with the elevation helpers. See Hillshade → Custom lighting shader.