Surface3DProjectionShaderProgram

Surface-projection shader that drapes a source image onto terrain via a 4x4 camera-frustum matrix in WGS84 ECEF, evaluated per fragment. Companion to SurfaceQuadShaderProgram (the 2D-homography path); used by the 3D path on earth.worldwind.shape.ProjectedMediaSurface when the shape carries an imageProjection matrix.

Pipeline per terrain tile:

• CPU pre-multiplies the world-space imageProjection by the tile's local-frame translation, producing imageProjectionLocal - a tile-local matrix that maps a terrain vertex's tile-local 3D position to image clip space. Keeps the per-vertex math in float-precise small magnitudes; world ECEF coordinates would lose sub-metre precision in single-precision float.

• Vertex shader emits gl_Position via the standard mvpMatrix AND a perspective imageClip varying = imageProjectionLocal * vec4(pointA.xyz, 1.0).

• Fragment shader divides imageClip.xy / imageClip.w for perspective-correct UV in image space, applies texCoordMatrix (e.g. the source texture's vertical flip), samples the source texture. Discards fragments behind the camera (imageClip.w <= 0) and outside the unit-square image bounds (UV < 0 or > 1) so only terrain inside the camera's frustum receives the image.

No skin-texture stage: this shader runs the source texture directly against the terrain triangulation. That trades the surface-drawable's batching ability for correct projection on relief-heavy terrain.

Inheritors