https://github.com/miloyip/svpng

Minimalistic C function for saving RGB/RGBA image as uncompressed PNG.
https://github.com/miloyip/svpng

Last synced: about 2 months ago
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Minimalistic C function for saving RGB/RGBA image as uncompressed PNG.

• Host: GitHub
• URL: https://github.com/miloyip/svpng
• Owner: miloyip
• License: bsd-3-clause
• Created: 2017-04-23T07:50:26.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2022-01-08T11:00:56.000Z (over 2 years ago)
• Last Synced: 2024-06-21T20:35:27.937Z (3 months ago)
• Language: C++
• Homepage:
• Size: 294 KB
• Stars: 640
• Watchers: 27
• Forks: 120
• Open Issues: 5
• Metadata Files:
  • Readme: readme.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# svpng v0.1.1

A minimalistic C function for saving RGB/RGBA image into uncompressed PNG.

Copyright (C) 2017 Milo Yip. All rights reserved.

# Features

* RGB or RGBA color format

* Single function

* 32 lines of ANSI C code

* No dependency

* Customizable output stream (default with C file descriptor)

# Usage

By default, `svpng()` function has the following declaration:

~~~c

/*!

    \brief Save a RGB/RGBA image in PNG format.

    \param out Output stream (by default using file descriptor).

    \param w Width of the image. (<16383)

    \param h Height of the image.

    \param img Image pixel data in 24-bit RGB or 32-bit RGBA format.

    \param alpha Whether the image contains alpha channel.

*/

void svpng(FILE* out, unsigned w, unsigned h, const unsigned char* img, int alpha);

~~~

Basically, you `fopen()` a binary file for writing, then call this function with the image data. The pixels are packed linearly from top to bottom, left to right.

For 24-bit RGB format (with `alpha = 0`), the R, G, B components are stored in `img[(y * w + x) * 3]`, `img[(y * w + x) * 3 + 1]`, `img[(y * w + x) * 3 + 2]` respectively.

For 32-bit RGBA format  (with `alpha != 0`), the R, G, B, A components are stored in `img[(y * w + x) * 4]`, `img[(y * w + x) * 4 + 1]`, `img[(y * w + x) * 4 + 2]`, `img[(y * w + x) * 4 + 3]` respectively.

## Example

[example.c](example.c) saves a RGB and a RGBA PNG.

~~~c

void test_rgb(void) {

    unsigned char rgb[256 * 256 * 3], *p = rgb;

    unsigned x, y;

    FILE *fp = fopen("rgb.png", "wb");

    for (y = 0; y < 256; y++)

        for (x = 0; x < 256; x++) {

            *p++ = (unsigned char)x;    /* R */

            *p++ = (unsigned char)y;    /* G */

            *p++ = 128;                 /* B */

        }

    svpng(fp, 256, 256, rgb, 0);

    fclose(fp);

}

void test_rgba(void) {

    unsigned char rgba[256 * 256 * 4], *p = rgba;

    unsigned x, y;

    FILE* fp = fopen("rgba.png", "wb");

    for (y = 0; y < 256; y++)

        for (x = 0; x < 256; x++) {

            *p++ = (unsigned char)x;                /* R */

            *p++ = (unsigned char)y;                /* G */

            *p++ = 128;                             /* B */

            *p++ = (unsigned char)((x + y) / 2);    /* A */

        }

    svpng(fp, 256, 256, rgba, 1);

    fclose(fp);

}

int main(void) {

    test_rgb();

    test_rgba();

    return 0;

}

~~~

## Compilation

~~~

gcc example.c && ./a.out

~~~

## Output

![rgb.png](rgb.png)

![rgba.png](rgba.png)

# Customizability

User can define the following macros before including `svpng.inc`.

| Macro           | Default         | Description |

|-----------------|-----------------|-------------|

| `SVPNG_LINKAGE` | (empty)         | Linkage of `svpng()` function, e.g. `inline`, `static`, `extern "C"`, etc. |

| `SVPNG_OUTPUT`  | `FILE* out`     | Output stream parameter, e.g. `std::ostream& os`, `std::vector& buffer`, etc. |

| `SVPNG_PUT(u)`  | `fputc(u, out)` | Output a byte into stream, e.g. `os.put(u)`, `buffer.push_back(u)`, etc. |