Let the fused shader sample a window of a larger source

A photograph larger than one texture has to be developed from a part of
it or from a reduced copy of it. The generated prologue measured the frame
by the bound texture, so either would have moved every crop, warp and
grain seed. Two uniform vec4s now say which part of the frame the texture
holds and how large the frame is; the sampler maps into the texture
through to_window, and a texture holding the whole frame samples exactly
as before ((uv - 0) / 1 is uv to the bit).

core/dr-pipeline/src/lib.rs

@@ -68,6 +68,7 @@ pub use lens::{compose_warps, ComposedWarp, LensProfile, Tca, Warp};
 pub use operation::{
     compose, compose_with_framing, Affects, ComposedShader, Helper, Invalidation, Operation,
     OutputMode, Stage, Uniform, CLIP_ONSET, RESERVED_UNIFORM_FIELDS, SAMPLE_CACHE_UNIFORM_OFFSET,
+    SOURCE_WINDOW_UNIFORM_FIELDS, SOURCE_WINDOW_UNIFORM_OFFSET, WHOLE_SOURCE_WINDOW,
 };
 pub use preset::{LibraryParseError, NameError, Preset, PresetLibrary, Reach, Scope};
 pub use sidecar::{Sidecar, Version};