Read/Write Radiance shared-exponent RGBE HDR image files

Reading

Read with (READ-HDR-FILE FILE-NAME &key FORMAT Y-UP) or (READ-HDR-STREAM STREAM &key FORMAT Y-UP).

FILE-NAME is a pathname designator for an HDR file.

STREAM is an open (unsigned-byte 8) input stream.

FORMAT is either :RGB9-E5(default) or :FLOAT. If it is :FLOAT, data will be returned as single-floats, if :RGB9-E5 it will be returned as (unsigned-byte 32) containing GL-style RGB9-E5 data.

Y-UP specifies that data should be returned as GL-style lower-left origin (bottom row first), otherwise it is returned with upper-left origin (top-row first).

Both functions return an HDR-FILE object with following accessors:

WIDTH = width of image in pixels

HEIGHT = height of image in rows

DATA = vector of (UNSIGNED-BYTE 32) with 1 element per pixel or SINGLE-FLOAT with 3 elements per pixel, depending on requested FORMAT when loading.

ORIGIN = :UPPER-LEFT or :LOWER-LEFT depending on requested Y-UP when loading.

GL-PIXEL-TYPE, GL-PIXEL-FORMAT, GL-INTERNAL-FORMAT = values suitable to pass to cl-opengl when creating/uploading textures from data, :unsigned-int-5-9-9-9-rev :rgb :rgb9-e5 or :float :rgb :rgb32f depending on FORMAT

EXPOSURE = (product of) EXPOSURE header value(s) in HDR file, or 1.0 if none specified. Usually 1.0.

Writing

Write with (WRITE-HDR-FILE FILE-NAME HDR &key UNCOMPRESSED IF-EXISTS IF-DOES-NOT-EXIST) or (WRITE-HDR-STREAM STREAM HDR &key UNCOMPRESSED)

FILE-NAME is a pathname designator for an HDR file to be written.

STREAM is an open (unsigned-byte 8) output stream.

HDR is an HDR-FILE object, with at least WIDTH, HEIGHT, DATA, GL-PIXEL-TYPE, and ORIGIN specified.

If UNCOMPRESSED is true, write scanlines as uncompressed RGBE instead of new-style RLE-compressed data.

IF-EXISTS (default :error) and IF-DOES-NOT-EXIST (default :create) are passed to CL:OPEN