Changeset 35578 in project

Timestamp:

06/11/18 20:37:54 (16 months ago)

Author:

kristianlm

Message:

obs: stb-image-resize using markdown-svnwiki

File:

• wiki/eggref/4/stb-image-resize (modified) (1 diff)

wiki/eggref/4/stb-image-resize

@@ -1 @@
-== chicken-stb-image
+== stb-image-resize
 [[toc:]]
-This is a [[http://call-cc.org|CHICKEN]] egg that wraps [[https://github.com/nothings/stb|stb_image.h]] version 2.19 from
-Sean Barrett and friends. It works on [[http://call-cc.org|CHICKEN]] 4 and 5.
+This is a [[http://call-cc.org|CHICKEN]] egg that wraps [[https://github.com/nothings/stb|stb''image''resize.h]] version 0.95
+from Jorge L Rodriguez and friends. It works on [[http://call-cc.org|CHICKEN]] 4 and 5.
 
 
 == API
 [[toc:]]
-<procedure> (read-image #!key channels)</procedure>
-<procedure> (load-image u8vector #!key channels)</procedure>
+<procedure> (image-resize pixels width height channels target-width target-height #!key filter region alpha-channel)</procedure>
 
-Decodes an image into raw pixel data. {{read-image}} reads the image
-from from {{(current-input-port)}} while {{load-image}} gets this from the
-provided u8vector. The image type is detected by content, and may be:
-JPEG, PNG, TGA, BMP, PSD, GIF, HDR, PIC, PNM as explained in the
-heading comments of {{stb_image.h}}.
+Takes in raw {{pixels}} (a srfi-4 u8/u16/u32/f32vector) of size
+{{width}}''{{height}}''{{channels}} and returns raw pixels after resizing. The
+returned type is the same as {{pixels}}' of size
+{{target-width}}''{{target-height}}''{{channels}}.
 
-Both procedures return 4 values:
+{{channels}} must be an integer between 0 and 64 and keys are processed
+as follows.
 
-# raw pixel data (as u8vector)
-# width
-# height
-# number of channels
-
-You can force the number of channels with the {{channels}} keyword. If
-{{channels}} is {{#f}} or not given, the number of channels in the
-original image will be used.
-
-The size of the pixel data blob is always {{(* width height channels)}}
-bytes. The first pixel is the top-left-most in the image. Each pixel
-is {{channel}} number of bytes long. The number of channels define the
-pixel color, interleaved as follows:
-
-# grey
-# grey, alpha
-# red, green, blue
-# red, green, blue, alpha
-
-Note that [[https://github.com/nothings/stb|stb_image.h]]'s {{hdr}} and {{pnm}} support only works with
-{{load-image}}.
-
-<procedure> (read-image-info)</procedure>
-<procedure> (load-image-info blob)</procedure>
-
-Like {{read-image}} and {{load-image}}, but does not load pixel data and
-should be faster. Returns three values:
-
-# width
-# height
-# number of channels
+* {{filter:}} one of {{box}}, {{triangle}}, {{cubicbspline}}, {{catmullrom}} or
+  {{mitchell}}. The default uses {{catmullrom}} for up-sampling and
+  {{mitchell}} for down-sampling.
+* {{region:}} a vector of 4 elements {{s0 t0 s1 t1}}, representing the
+  UV-coordinates to use as source image. This can be used to crop the
+  image. These values must be in the range of {{[0, 1]}} and represent
+  the fraction of the input image. {{#(0 0 0.5 1)}}, for example, cuts
+  off the right half of the image.
+* {{alpha-channel:}} index of channel which is the alpha channel in the
+  image. supply {{#f}} (default) for no alpha channel.
 
 
-=== Examples
-For quick testing, you can read PNGs from ImageMagick's {{convert}}:
+== Examples
+[[toc:]]
+You can try {{example-thumbnail.scm}} like this:
 
-    $ convert -size 4x4 xc:blue -draw 'line 0,0 4,4' png:- | csi -R stb-image -p '(read-image)'
-    #u8(0 0 0     0 0 234   0 0 255   0 0 255
-        0 0 234   0 0 0     0 0 234   0 0 255
-        0 0 255   0 0 234   0 0 0     0 0 234
-        0 0 255   0 0 255   0 0 234   0 0 0)
-    4
-    4
-    3
+[[image:example.png?raw=true|screenshot of running example-thumbnail.scm]]
 
-Which reveal the black line along the diagonal and informs that the
-image is 4x4 with 3-channels.
+Or turn a 4x1 greyscale image into a single pixel like this:
 
+{{
+$ csi -R srfi-4 -R stb-image-resize -p '(image-resize (f32vector 0 4 8) 3 1 1   1 1)'
+#f32(4.0)
+}}
+