misc0110 / libattopng

A minimal C library to write uncompressed PNG images

libattopng

libattopng is a minimal C library to create uncompressed PNG images. It is cross-platform compatible, has no dependencies and a very small footprint of less than 10kB. The library supports palette, grayscale as well as raw RGB images all with and without transparency.

Usage

Using libattopng is as simple as adding both libattopng.h and libattopng.c to your project. Independent of the used standard (from C89 to C11), the code will compile without warnings. The library does not require any special flags to compile.

Example

Color gradient with alpha

#define RGBA(r, g, b, a) ((r) | ((g) << 8) | ((b) << 16) | ((a) << 24))

libattopng_t* png = libattopng_new(250, 200, PNG_RGBA);

int x, y;
for (y = 0; y < 200; y++) {
  for (x = 0; x < 250; x++) {
    libattopng_set_pixel(png, x, y, RGBA(x & 255, y & 255, 128, (255 - ((x / 2) & 255))));
  }
}
libattopng_save(png, "test_rgba.png");
libattopng_destroy(png);

Stripes with palette and alpha

#define RGBA(r, g, b, a) ((r) | ((g) << 8) | ((b) << 16) | ((a) << 24))

// ceate palette image
libattopng_t *png = libattopng_new(256, 256, PNG_PALETTE);
uint32_t palette[] = {RGBA(0, 0, 0xff, 0xff), RGBA(0, 0xff, 0, 0x80), RGBA(0xff, 0, 0, 0xff), RGBA(0xff, 0, 0xff, 0x80)};
// 4 colors: blue, green (50% alpha), red, cyan (50% alpha) 
libattopng_set_palette(png, palette, 4);

int x, y;
for (y = 0; y < 256; y++) {
  for (x = 0; x < 256; x++) {
    libattopng_set_pixel(png, x, y, (x % 16) / 4);
  }
}

libattopng_save(png, "test_palette.png");
libattopng_destroy(png);

More examples

See test.c for more examples.

API documentation

Brief content:

Functions:

libattopng_new: Create a new, empty PNG image to be used with all other functions.

libattopng_destroy: Destroys the reference to a PNG image and free all associated memory.

libattopng_set_palette: Sets the image's palette if the image type is PNG_PALETTE.

libattopng_set_pixel: Sets the pixel's color at the specified position

libattopng_get_pixel: Returns the pixel's color at the specified position

libattopng_start_stream: Set the start position for a batch of pixels

libattopng_put_pixel: Sets the pixel of the current pixel within a stream and advances to the next pixel

libattopng_get_data: Returns the image as PNG data stream

libattopng_save: Saves the image as a PNG file

Functions

The module libattopng.h defines the following functions.

Function libattopng_new

Create a new, empty PNG image to be used with all other functions.

It's the callers responsibility to free the data structure. See libattopng_destroy

Parameters:

• width: The width of the image in pixels

• height: The height of the image in pixels

• type: The type of image. Possible values are

    - PNG_GRAYSCALE (8bit grayscale),
    - PNG_GRAYSCALE_ALPHA (8bit grayscale with 8bit alpha),
    - PNG_PALETTE (palette with up to 256 entries, each 32bit RGBA)
    - PNG_RGB (24bit RGB values)
    - PNG_RGBA (32bit RGB values with alpha)
  

Returns:

• reference to a PNG image to be used with all other functions or NULL on error. Possible errors are: - Out of memory - Width and height combined exceed the maximum integer size

Function libattopng_destroy

Destroys the reference to a PNG image and free all associated memory.

Parameters:

• png: Reference to the image

Returns:

No return

Function libattopng_set_palette

Sets the image's palette if the image type is PNG_PALETTE.

Parameters:

• png: Reference to the image
• palette: Color palette, each entry contains a 32bit RGBA value
• length: Number of palette entries

Returns:

• 0 on success, 1 if the palette contained more than 256 entries

Function libattopng_set_pixel

Sets the pixel's color at the specified position

Parameters:

• png: Reference to the image

• x: X coordinate

• y: Y coordinate

• color: The pixel value, depending on the type this is

    - the 8bit palette index (PNG_PALETTE)
    - the 8bit gray value (PNG_GRAYSCALE)
    - a 16bit value where the lower 8bit are the gray value and
      the upper 8bit are the opacity (PNG_GRAYSCALE_ALPHA)
    - a 24bit RGB value (PNG_RGB)
    - a 32bit RGBA value (PNG_RGBA)
  

If the coordinates are not within the bounds of the image, the functions does nothing.

Returns:

No return

Function libattopng_get_pixel

Returns the pixel's color at the specified position

Parameters:

• png: Reference to the image
• x: X coordinate
• y: Y coordinate

Returns:

• The pixel value, depending on the type this is

    - the 8bit palette index (PNG_PALETTE)
    - the 8bit gray value (PNG_GRAYSCALE)
    - a 16bit value where the lower 8bit are the gray value and
      the upper 8bit are the opacity (PNG_GRAYSCALE_ALPHA)
    - a 24bit RGB value (PNG_RGB)
    - a 32bit RGBA value (PNG_RGBA)
    - 0 if the coordinates are out of bounds
  

Function libattopng_start_stream

Set the start position for a batch of pixels

Parameters:

• png: Reference to the image
• x: X coordinate
• y: Y coordinate

Returns:

No return

See:

libattopng_put_pixel

Function libattopng_put_pixel

Sets the pixel of the current pixel within a stream and advances to the next pixel

Parameters:

• png: Reference to the image

• color: The pixel value, depending on the type this is

    - the 8bit palette index (PNG_PALETTE)
    - the 8bit gray value (PNG_GRAYSCALE)
    - a 16bit value where the lower 8bit are the gray value and
      the upper 8bit are the opacity (PNG_GRAYSCALE_ALPHA)
    - a 24bit RGB value (PNG_RGB)
    - a 32bit RGBA value (PNG_RGBA)
  

Returns:

No return

Function libattopng_get_data

Returns the image as PNG data stream

Parameters:

• png: Reference to the image
• len: The length of the data stream is written to this output parameter

Returns:

• A reference to the PNG output stream

The data stream is free'd when calling \ref libattopng_destroy and must not be free'd be the caller

Function libattopng_save

Saves the image as a PNG file

Parameters:

• png: Reference to the image
• filename: Name of the file

Returns:

• 0 on success, 1 on error