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Add the epsilon value into the alpha instead of using an if statement. It's a tiny bit faster and it can be removed afterwards.

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This commit is contained in:
Jorge Rodriguez 2014-09-09 22:47:53 -07:00
parent 1d5c902e2e
commit 17b931047c
1 changed files with 6 additions and 3 deletions
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9
stb_image_resize.h
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@ -1040,10 +1040,9 @@ static void stbir__decode_scanline(stbir__info* stbir_info, int n)
for (x = -stbir__get_filter_pixel_margin_horizontal(stbir_info); x < max_x; x++) for (x = -stbir__get_filter_pixel_margin_horizontal(stbir_info); x < max_x; x++)
{ {
int decode_pixel_index = x * channels; int decode_pixel_index = x * channels;
float alpha = decode_buffer[decode_pixel_index + alpha_channel];
if (alpha == 0) // If the alpha value is 0 it will clobber the color values. Make sure it's not.
alpha = decode_buffer[decode_pixel_index + alpha_channel] = (float)1 / 17179869184; // 1/2^34 should be small enough that it won't affect anything. float alpha = (decode_buffer[decode_pixel_index + alpha_channel] += (float)1 / 17179869184); // 1/2^34 should be small enough that it won't affect anything.
for (c = 0; c < channels; c++) for (c = 0; c < channels; c++)
{ {
@ -1226,12 +1225,16 @@ static void stbir__encode_scanline(stbir__info* stbir_info, int num_pixels, void
for (x=0; x < num_pixels; ++x) for (x=0; x < num_pixels; ++x)
{ {
int pixel_index = x*channels; int pixel_index = x*channels;
float alpha = encode_buffer[pixel_index + alpha_channel]; float alpha = encode_buffer[pixel_index + alpha_channel];
STBIR__DEBUG_ASSERT(alpha > 0); STBIR__DEBUG_ASSERT(alpha > 0);
float reciprocal_alpha = alpha ? 1.0f / alpha : 0; float reciprocal_alpha = alpha ? 1.0f / alpha : 0;
for (n = 0; n < channels; n++) for (n = 0; n < channels; n++)
if (n != alpha_channel) if (n != alpha_channel)
encode_buffer[pixel_index + n] *= reciprocal_alpha; encode_buffer[pixel_index + n] *= reciprocal_alpha;
// We added in a small epsilon to prevent the color channel from being deleted with zero alpha. Remove it now.
encode_buffer[pixel_index + alpha_channel] -= (float)1 / 17179869184; // 1/2^34 should be small enough that it won't affect anything.
} }
} }