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even more resampling notes

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Sean Barrett 2014-07-22 12:45:24 -07:00
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39
docs/stb_resample_ideas.txt
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@ -8,7 +8,7 @@ library back to C:
2. 2.
@VinoBS Another option is to just port @richgel999's C++ library to C/stb: https://code.google.com/p/imageresampler/source/browse/#svn%2FtrunkConsider three cases just to suggest the spectrum Consider three cases just to suggest the spectrum
of possiblities: of possiblities:
a) linear upsample: each output pixel is a weighted sum a) linear upsample: each output pixel is a weighted sum
@ -75,8 +75,24 @@ optimal is to do whichever axis is smaller first, but I don't
think we have to care about doing that right.) think we have to care about doing that right.)
Now, you probably want to avoid memory allocations (since you're passing Now, you can either:
in the target buffer already), so instead of using a scanline-width
1. malloc the temp memory
2. alloca it
3. allocate a fixed amount on the stack
4. let the user pass it in
I forbid #2 in stb libraries for portability.
If you're not allocating the output image, but rather requiring
the user to pass it in, it's probably worth trying to avoid #1
because people always want to use stb libs without any memory
allocations for various reason. (Note that most stb libs go
crazy with memory allocations--you shouldn't use stb_image
in a console game--but I've tried to avoid it more in newer
libs.)
The way #3 would work is instead of using a scanline-width
temp buffer, use some fixed-width temp buffer that's W pixels, temp buffer, use some fixed-width temp buffer that's W pixels,
and scale the image in vertical stripes that are that wide. and scale the image in vertical stripes that are that wide.
Suppose you make the temp buffers 256 wide; then an upsample Suppose you make the temp buffers 256 wide; then an upsample
@ -86,6 +102,9 @@ strips (from a 256-pixel width strip). Note this limits
the max down/upsampling to be ballpark 256x along the the max down/upsampling to be ballpark 256x along the
horizontal axis. horizontal axis.
In the following, I do #3 and allow #4 for cases where #3 is
too small, but it's not the only possibility:
Function prototypes: Function prototypes:
@ -101,11 +120,11 @@ the lowest-level one could be:
stb_resample_arbitrary(void *dst, stbr_type dst_type, int dst_width, int dst_height, int dst_stride_in_bytes, stb_resample_arbitrary(void *dst, stbr_type dst_type, int dst_width, int dst_height, int dst_stride_in_bytes,
void const *src, stbr_type src_type, int src_width, int src_height, int src_stride_in_bytes, void const *src, stbr_type src_type, int src_width, int src_height, int src_stride_in_bytes,
float s0, float t0, float s1, float t1, // range of source to use, 0..1 in GPU texture-coordinate style
int channels, int channels,
int nonpremul_alpha_channel_index, int nonpremul_alpha_channel_index,
stbr_wrapmode wrap, // clamp, wrap, mirror stbr_wrapmode wrap, // clamp, wrap, mirror
stbr_filter filter, stbr_filter filter,
float s0, float t0, float s1, float t1, // range of source to use, 0..1 in GPU texture-coordinate style
void *tempmem, size_t tempmem_size_in_bytes); void *tempmem, size_t tempmem_size_in_bytes);
And there would be a bunch of convenience functions in-between those two levels. And there would be a bunch of convenience functions in-between those two levels.
@ -113,6 +132,12 @@ And there would be a bunch of convenience functions in-between those two levels.
Some notes: Some notes:
s0,t0,s1,t1:
this allows fine subpixel-positioning and subpixel-resizing in an explicit way without
things having to be exact pixel multiples. it allows people to pseudo-stream
images by computing "tiles" of images a bit at a time without forcing those
tiles to quantize their source data.
nonpremul_alpha_channel_index: nonpremul_alpha_channel_index:
if this is negative, no channels are processed specially if this is negative, no channels are processed specially
if this is non-negative, then it's the index of the alpha channel, if this is non-negative, then it's the index of the alpha channel,
@ -124,12 +149,6 @@ Some notes:
pass in which channels serve as alpha channels for which other pass in which channels serve as alpha channels for which other
channels, but eh. channels, but eh.
s0,t0,s1,t1:
this allows fine subpixel-positioning and subpixel-resizing in an explicit way without
things having to be exact pixel multiples. it allows people to pseudo-stream
images by computing "tiles" of images a bit at a time without forcing those
tiles to quantize their source data.
tempmem, tempmem_size: tempmem, tempmem_size:
all functions will needed tempmem, but they can allocate a fixed tempmem buffer all functions will needed tempmem, but they can allocate a fixed tempmem buffer
on the stack. providing an API that allows overriding the amount of tempmem on the stack. providing an API that allows overriding the amount of tempmem