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stb_image_write: fix linker errors in HDR image functions when STBI_WRITE_NO_STDIO is defined #1959

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stb_image_write: fix linker errors in HDR image functions when STBI_WRITE_NO_STDIO is defined #1959

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cb00f2b
stb_image_write: fix linker errors when writing HDR images with STBI_…
sanjay-nambiar Jun 2, 2026
aeb6907
stb_image_write: update int to string function to a simpler one
sanjay-nambiar Jun 4, 2026
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42 changes: 33 additions & 9 deletions stb_image_write.h
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,7 @@
github:ignotion
Adam Schackart
Andrew Kensler
Sanjay Nambiar

LICENSE

Expand Down Expand Up @@ -634,8 +635,6 @@ STBIWDEF int stbi_write_tga(char const *filename, int x, int y, int comp, const

#define stbiw__max(a, b) ((a) > (b) ? (a) : (b))

#ifndef STBI_WRITE_NO_STDIO

static void stbiw__linear_to_rgbe(unsigned char *rgbe, float *linear)
{
int exponent;
Expand Down Expand Up @@ -758,24 +757,48 @@ static void stbiw__write_hdr_scanline(stbi__write_context *s, int width, int nco
}
}

static int stbiw__u32_to_string(unsigned int value, char* dest)
{
char buff[12] = {0};
char* s = &buff[11];
int len = 0;

do {
*--s = '0' + (value % 10);
} while(value /= 10);

len = 11 - (s - buff);
memcpy(dest, s, len);
return len;
}

static int stbi_write_hdr_core(stbi__write_context *s, int x, int y, int comp, float *data)
{
const char* header_str_part1 = "EXPOSURE= 1.0000000000000\n\n-Y ";
const char* header_str_part2 = " +X ";
const int header_str_part1_len = strlen(header_str_part1);
const int header_str_part2_len = strlen(header_str_part2);

if (y <= 0 || x <= 0 || data == NULL)
return 0;
else {
// Each component is stored separately. Allocate scratch space for full output scanline.
unsigned char *scratch = (unsigned char *) STBIW_MALLOC(x*4);
int i, len;
int i;
char buffer[128];
char* dst = buffer;
char header[] = "#?RADIANCE\n# Written by stb_image_write.h\nFORMAT=32-bit_rle_rgbe\n";
s->func(s->context, header, sizeof(header)-1);

#ifdef __STDC_LIB_EXT1__
len = sprintf_s(buffer, sizeof(buffer), "EXPOSURE= 1.0000000000000\n\n-Y %d +X %d\n", y, x);
#else
len = sprintf(buffer, "EXPOSURE= 1.0000000000000\n\n-Y %d +X %d\n", y, x);
#endif
s->func(s->context, buffer, len);
memcpy(dst, header_str_part1, header_str_part1_len);
dst += header_str_part1_len;
dst += stbiw__u32_to_string(y, dst);
memcpy(dst, header_str_part2, header_str_part2_len);
dst += header_str_part2_len;
dst += stbiw__u32_to_string(x, dst);
*dst++ = '\n';

s->func(s->context, buffer, dst - buffer);

for(i=0; i < y; i++)
stbiw__write_hdr_scanline(s, x, comp, scratch, data + comp*x*(stbi__flip_vertically_on_write ? y-1-i : i));
Expand All @@ -791,6 +814,7 @@ STBIWDEF int stbi_write_hdr_to_func(stbi_write_func *func, void *context, int x,
return stbi_write_hdr_core(&s, x, y, comp, (float *) data);
}

#ifndef STBI_WRITE_NO_STDIO
STBIWDEF int stbi_write_hdr(char const *filename, int x, int y, int comp, const float *data)
{
stbi__write_context s = { 0 };
Expand Down