Image extension

Loading and Saving

Save image files and load them again.

Connecting Image to files

save_image saves an Image to a file; load_image reads one. Supported formats such as PNG and JPEG depend on the Qt image plugins supplied with the application.

Try it first

Example · example1.cpp

#include <small/image.h>

void small_main()
{
    Image made(200, 120, Cyan);

    for (int y = 30; y < 90; y++)
        for (int x = 40; x < 160; x++)
            made.set_pixel(x, y, Magenta);

    save_image(made, "small_image_test.png");

    Image loaded = load_image("small_image_test.png");
    print("Loaded: ", loaded.width(), " x ", loaded.height());

    Window window;
    window.open(500, 300);

    while (window.is_open())
    {
        window.clear(Black);
        draw_image(window, loaded, 150, 80);
        window.show();
    }
}

The filename chooses the format

An extension such as in save_image(image, "picture.png") chooses the saved format. Small reports a runtime error if a file cannot be opened or saved.

draw_image composites the loaded image's alpha information.

One step further

Example · example2.cpp

#include <small/image.h>

void small_main()
{
    Image image(120, 80, Yellow);
    save_image(image, "picture.png");

    Image copy = load_image("picture.png");

    print(copy.width(), " x ", copy.height());
}

The basic Image workflow is complete

You can create or load an image, inspect or edit its pixels, draw it, and save it. These operations are ordinary C++ library APIs designed for use outside Small IDE too.

Exercise — Save and read

Save a 50 × 50 Cyan image as cyan.png, then load it into a new Image.

Exercise starter · exercise1_starter.cpp

#include <small/image.h>
void small_main()
{
    Image image(50, 50, Cyan);
    // Save and load.
}

Hint

Use Image loaded = load_image("cyan.png");.

show solution

#include <small/image.h>
void small_main()
{
    Image image(50, 50, Cyan);
    save_image(image, "cyan.png");
    Image loaded = load_image("cyan.png");
    print(loaded.width(), " x ", loaded.height());
}

Exercise — Edit a file

Create and save an image, load it again, change (0, 0) to Magenta, and save under a different name.

Exercise starter · exercise2_starter.cpp

#include <small/image.h>
void small_main()
{
    Image image(20, 20, White);
    save_image(image, "original.png");
    // Load, change one pixel, and save as changed.png.
}

Hint

Using a second filename preserves the original file.

show solution

#include <small/image.h>
void small_main()
{
    Image image(20, 20, White);
    save_image(image, "original.png");
    Image changed = load_image("original.png");
    changed.set_pixel(0, 0, Magenta);
    save_image(changed, "changed.png");
}

Share your finished program

Small Steps VII — Share Your Program shows how to make a Windows package. Include any image files your program loads with Add Files, then share the whole folder as a ZIP.