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@@ -60,3 +60,69 @@ horizontal axis.
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+Function prototypes:
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+
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+the highest-level one could be:
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+
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+ stb_resample_8bit(uint8_t *dest, int dest_width, int dest_height,
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+ uint8_t const *src , int src_width, int src_height,
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+ int channels,
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+ stbr_filter filter);
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+
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+the lowest-level one could be:
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+
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+ stb_resample_arbitrary(void *dest, stbr_type dest_type, int dest_width, int dest_height, int dest_stride_in_bytes,
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+ void const *src , stbr_type src_type, int src_width, int src_height, int src_stride_in_bytes,
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+ int channels,
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+ int nonpremul_alpha_channel_index,
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+ stbr_wrapmode wrap, // clamp, wrap, mirror
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+ stbr_filter filter,
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+ float s0, float t0, float s1, float t1, // range of source to use, 0..1 in GPU texture-coordinate style
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+ void *tempmem, size_t tempmem_size_in_bytes);
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+
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+And there would be a bunch of convenience functions at in-between levels.
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+
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+
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+Some notes:
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+
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+ Intermediate-level functions should be provided for each source type & same dest type
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+ so that the code is typesafe; only when people fall back to stb_resample_arbitrary should
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+ they be at risk for type unsafety. (One way to deal with the explosion of functions of
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+ every possible type would be to define one function for each input type, and accept three
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+ separate output pointers, one for each type, only one of which can be non-NULL.)
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+
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+ nonpremul_alpha_channel_index:
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+ if this is negative, no channels are processed specially
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+ if this is non-negative, then it's the index of the alpha channel,
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+ and the image should be treated as non-premultiplied alpha that
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+ needs to be resampled accounting for this (weight the sampling
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+ by the alpha channel, i.e. premultiply, filter, unpremultiply).
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+ this mechanism only allows one alpha channel and ALL channels
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+ are scaled by it; an alternative would be to find some way to
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+ pass in which channels serve as alpha channels for which other
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+ channels, but eh.
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+
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+ s0,t0,s1,t1:
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+ this allows fine subpixel-positioning and subpixel-resizing in an explicit way without
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+ things having to be exact pixel multiples. it allows people to pseudo-stream
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+ images by computing "tiles" of images a bit at a time without forcing those
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+ tiles to quantize their source data.
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+
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+ tempmem, tempmem_size
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+ all functions will needed tempmem, but they can allocate a fixed tempmem buffer
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+ on the stack. providing an API that allows overriding the amount of tempmem
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+ available allows people to process arbitrarily large images. the return
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+ value for the function could be 0 on success or non-0 being the size of
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+ tempmem needed.
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+
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+
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+
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+
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+Reference:
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+
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+Cubic sampling function for seperable cubic:
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+ f(x) = (a+2)*x^3 - (a+3)*x^2 + 1 for 0 <= x <= 1
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+ f(x) = a*x^3 - 5*a*x^2 + 8*a*x - 4*a for 1 < x <= 2
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+ f(x) = 0 otherwise
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+ "a" is configurable, try -1/2 (from http://pixinsight.com/forum/index.php?topic=556.0 )
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+
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Sean Barrett