Nuklear/Readme.md

# GUI
This is a bloat free stateless immediate mode graphical user interface toolkit
written in ANSI C. It was designed as a embeddable user interface for graphical
application and does not have any direct dependencies. The main premise of this
toolkit is to be as stateless and simple but at the same time as powerful as
possible with fast streamlined development speed in mind.

## Features
- Immediate mode graphical user interface toolkit
- Written in C89 (ANSI C)
- Small codebase (~3kLOC)
- Focus on portability and minimal internal state
- Suited for embedding into graphical applications
- No global hidden state
- No direct dependencies (not even libc!)
- Full memory management control
- Renderer and platform independent
- Configurable
- UTF-8 support

## Limitations
- Does NOT provide os window/input management
- Does NOT provide a renderer backend
- Does NOT implement a font library  
Summary: It is only responsible for the actual user interface

## Gallery
![gui screenshot](/screen/demo.png?raw=true)
![gui screenshot](/screen/config.png?raw=true)
![gui screenshot](/screen/config2.png?raw=true)

## Example
```c
struct gui_input input = {0};
struct gui_config config;
struct gui_font font = {...};
struct gui_memory memory = {...};
struct gui_command_buffer buffer;
struct gui_panel panel;

gui_default_config(&config);
gui_panel_init(&panel, 50, 50, 220, 170,
    GUI_PANEL_BORDER|GUI_PANEL_MOVEABLE|
    GUI_PANEL_CLOSEABLE|GUI_PANEL_SCALEABLE|
    GUI_PANEL_MINIMIZABLE, &config, &font);
gui_buffer_init_fixed(buffer, &memory, GUI_CLIP);

while (1) {
    gui_input_begin(&input);
    /* record input */
    gui_input_end(&input);

    struct gui_canvas canvas;
    struct gui_command_list list;
    struct gui_panel_layout layout;
    struct gui_memory_status status;

    gui_buffer_begin(&canvas, &buffer, window_width, window_height);
    gui_panel_begin(&layout, &panel, "Demo", &canvas, &input);
    gui_panel_row(&layout, 30, 1);
    if (gui_panel_button_text(&layout, "button", GUI_BUTTON_DEFAULT)) {
        /* event handling */
    }

    gui_panel_row(&layout, 30, 2);
    if (gui_panel_option(&layout, "easy", option == 0)) option = 0;
    if (gui_panel_option(&layout, "hard", option == 1)) option = 1;

    gui_panel_label(&layout, "input:", GUI_TEXT_LEFT);
    len = gui_panel_edit(&layout, buffer, len, 256, &active, GUI_INPUT_DEFAULT);
    gui_panel_end(&layout, &panel);
    gui_buffer_end(&list, &buffer, &canvas, &status);

    const struct gui_command *cmd = gui_list_begin(&list);
    while (cmd) {
        /* execute command */
        cmd = gui_list_next(&list, cmd);
    }
}
```
![gui screenshot](/screen/screen.png?raw=true)

## IMGUIs
Immediate mode in contrast to classical retained mode GUIs store as little state as possible
by using procedural function calls as "widgets" instead of storing objects.
Each "widget" function call takes hereby all its necessary data and immediately returns
the through the user modified state back to the caller. Immediate mode graphical
user interfaces therefore combine drawing and input handling into one unit
instead of separating them like retain mode GUIs.

Since there is no to minimal internal state in immediate mode user interfaces,
updates have to occur every frame which on one hand is more drawing expensive than classic
retained GUI implementations but on the other hand grants a lot more flexibility and
support for overall layout changes. In addition without any state there is no
duplicated state between your program, the gui and the user which greatly
simplifies code. Further traits of immediate mode graphic user interfaces are a
code driven style, centralized flow control, easy extensibility and
understandability.

### Input
The `gui_input` struct holds the user input over the course of the frame and
manages the complete modification of widget and panel state. Like the panel and
buffering, input is an immediate mode API and consist of an begin sequence
point with `gui_input_begin` and a end sequence point with `gui_input_end`.
All modifications can only occur between both of these
sequence points while all outside modifcation provoke undefined behavior.

```c
struct gui_input input = {0};
while (1) {
    gui_input_begin(&input);
    /* record input */
    gui_input_end(&input);
}
```

### Font
Since there is no direct font implementation in the toolkit but font handling is
still an aspect of a gui implemenatation the gui struct was introduced. It only
contains the bare minimum of what is needed for font handling with a handle to
your font structure, the font height and a callback to calculate the width of a
given string.

### Configuration
The gui toolkit provides a number of different attributes that can be
configured, like spacing, padding, size and color.
While the widget API even expects you to provide the configuration
for each and every widget the panel layer provides you with a set of
attributes in the `gui_config` structure. The structure either needs to be
filled by the user or can be setup with some default values by the function
`gui_default_config`. Modification on the fly to the `gui_config` struct is in
true immediate mode fashion possible and supported.

### Canvas
The Canvas is the abstract drawing interface between the GUI toolkit
and the user and contains drawing callbacks for the primitives
scissor, line, rectangle, circle, triangle, bitmap and text which need to be
provided by the user. Main advantage of using the raw canvas instead of using
buffering is that no memory to buffer all draw command is needed. Instead you
can directly draw each requested primitive. The downside is setting up the canvas
structure and the fact that you have to draw each primitive immediately.
Internally the canvas is used to implement the buffering of primitive draw
commands, but can be used to implement a different buffering scheme like
buffering vertexes instead of primitives.

### Buffering
For the purpose of deferred drawing or the implementation of overlapping panels
the command buffering API was added. The command buffer hereby holds a queue of
drawing commands for a number of primitives eg.: line, rectangle, circle,
triangle and text. The memory for the command buffer is provided by the user
in three possible ways. First by providing a fixed size memory block which
will be filled up until no memory is left.
The second way is extending the fixed size memory block by reallocating at the
end of the frame if the provided memory size was not sufficient.
The final and most complex way of memory management is by providing allocator
callbacks with alloc, realloc and free.
In true immediate mode fashion the buffering API is based around sequence
points with a begin sequence point `gui_buffer_begin` and a end sequence
point `gui_buffer_end` and modification of state between both points. Just
like the input API the buffer modification before the beginning or after the end
sequence point is undefined behavior.

```c
struct gui_allocator allocator = {...};
struct gui_memory_status status;
struct gui_command_list list;
struct gui_command_buffer buffer;
gui_buffer_init(buffer, &allocator, 2.0f, INITAL_SIZE, 0);

while (1) {
    struct gui_canvas canvas;
    gui_buffer_begin(&canvas, &buffer, window_width, window_height);
    /* add commands by using the canvas */
    gui_buffer_end(&list, buffer, &status);
}

```
For the purpose of implementing multible panels, sub buffers were implemented.
With sub buffers you can create one global buffer which owns the allocated memory
and sub buffers which directly reference the global buffer. The biggest
advantage is that you do not have to allocate a buffer for each panel and boil
down the memory management to a single buffer.

```c
struct gui_memory memory = {...};
struct gui_memory_status status;
struct gui_command_list list;
struct gui_command_buffer buffer;
gui_buffer_init_fixed(buffer, &memory);

while (1) {
    struct gui_canvas canvas;
    struct gui_command_buffer sub;

    gui_buffer_begin(NULL, &buffer, width, height);
    gui_buffer_lock(&canvas, &buffer, &sub, 0, width, height);
    /* add commands by using the canvas */
    gui_buffer_unlock(&list, &buffer, &sub, &canvas, NULL);
    gui_buffer_end(NULL, &buffer, NULL, &status);
}
```

### Widgets
The minimal widget API provides a number of basic widgets and is designed for
uses cases where no complex widget layouts or grouping is needed.
In order for the GUI to work each widget needs a canvas to
draw to, positional and widgets specific data as well as user input
and returns the from the user input modified state of the widget.

```c
struct gui_input input = {0};
struct gui_font font = {...};
struct gui_canvas canvas = {...};
struct gui_button style = {...};

while (1) {
    if(gui_button_text(&canvas, 0, 0, 100, 30, "ok", GUI_BUTTON_DEFAULT, &style, &input, &font))
        fprintf(stdout, "button pressed!\n");
}
```

### Panels
To further extend the basic widget layer and remove some of the boilerplate
code the panel was introduced. The panel groups together a number of
widgets but in true immediate mode fashion does not save any state from
widgets that have been added to the panel. In addition the panel enables a
number of nice features on a group of widgets like movement, scaling,
closing and minimizing. An additional use for panel is to further extend the
grouping of widgets into tabs, groups and shelfs.
The panel is divided into a `struct gui_panel` with persistent life time and
the `struct gui_panel_layout` structure with a temporary life time.
While the layout state is constantly modified over the course of
the frame, the panel struct is only modified at the immediate mode sequence points
`gui_panel_begin` and `gui_panel_end`. Therefore all changes to the panel struct inside of both
sequence points have no effect in the current frame and are only visible in the
next frame.

```c
struct gui_panel panel;
struct gui_config config;
struct gui_font font = {...}
struct gui_input input = {0};
struct gui_canvas canvas = {...};
gui_default_config(&config);
gui_panel_init(&panel, 50, 50, 300, 200, 0, &config, &font);

while (1) {
    struct gui_panel_layout layout;
    gui_panel_begin(&layout, &panel, "Demo", &canvas, &input);
    gui_panel_row(&layout, 30, 1);
    if (gui_panel_button_text(&layout, "button", GUI_BUTTON_DEFAULT))
        fprintf(stdout, "button pressed!\n");
    value = gui_panel_slider(&layout, 0, value, 10, 1);
    progress = gui_panel_progress(&layout, progress, 100, gui_true);
    gui_panel_end(&layout, &panel);
}
```

### Stack
While using basic panels is fine for a single movable panel or a big number of
static panels, it has rather limited support for overlapping movable panels. For
that to change the panel stack was introduced. The panel stack holds the basic
drawing order of each panel so instead of drawing each panel individually they
have to be drawn in a certain order. The biggest problem while creating the API
was that the buffer has to saved with the panel, but the type of the buffer is
not known beforehand since it is possible to create your own buffer type.
Therefore just the sequence of panels is managed and you either have to cast
from the panel to your own type, use inheritance in C++ or use the `container_of`
macro from the Linux kernel. For the standard buffer there is already a type
`gui_window` which contains the panel and the buffer output `gui_command_list`,
which can be used to implement overlapping panels.

```c
struct gui_window window;
struct gui_memory memory = {...};
struct gui_memory_status status;
struct gui_command_buffer buffer;
struct gui_config config;
struct gui_font font = {...}
struct gui_input input = {0};
struct gui_stack stack;

gui_buffer_init_fixed(buffer, &memory);
gui_default_config(&config);
gui_panel_init(&win.panel, 50, 50, 300, 200, 0, &config, &font);
gui_stack_clear(&stack);
gui_stack_push(&stack, &win.panel);

while (1) {
    struct gui_panel_layout layout;
    struct gui_canvas canvas;

    gui_buffer_begin(&canvas, &buffer, window_width, window_height);
    gui_panel_begin_stacked(&layout, &win.panel, &stack, "Demo", &canvas, &input);
    gui_panel_row(&layout, 30, 1);
    if (gui_panel_button_text(&layout, "button", GUI_BUTTON_DEFAULT))
        fprintf(stdout, "button pressed!\n");
    gui_panel_end(&layout, &win.panel);
    gui_buffer_end(&win.list, buffer, &status);

    /* draw each panel */
    struct gui_panel *iter = stack.begin;
    while (iter) {
        const struct gui_window *w = iter;
        const struct gui_command *cmd = gui_list_begin(&w->list);
        while (cmd) {
            /* execute command */
            cmd = gui_list_next(&w->list, cmd);
        }
        iter = iter->next;
    }
}
```

## FAQ
#### Where is the demo/example code?
The demo and example code can be found in the demo folder.
There is demo code for Linux(X11), Windows(win32) and OpenGL(SDL2, freetype).
As for now there will be no DirectX demo since I don't have experience
programming with DirectX but you are more than welcome to provide one.

#### Why did you use ANSI C and not C99 or C++?
Personally I stay out of all "discussions" about C vs C++ since they are totally
worthless and never brought anything good with it. The simple answer is I
personally love C and have nothing against people using C++ especially the new
iterations with C++11 and C++14.
While this hopefully settles my view on C vs C++ there is still ANSI C vs C99.
While for personal projects I only use C99 with all its niceties, libraries are
a little bit different. Libraries are designed to reach the highest number of
users possible which brings me to ANSI C as the most portable version.
In addition not all C compiler like the MSVC
compiler fully support C99, which finalized my decision to use ANSI C.

#### Why do you typedef your own types instead of using the standard types?
This Project uses ANSI C which does not have the header file `<stdint.h>`
and therefore does not provide the fixed sized types that I need. Therefore
I defined my own types which need to be set to the correct size for each
platform. But if your development environment provides the header file you can define
`GUI_USE_FIXED_SIZE_TYPES` to directly use the correct types.

#### Why is font/input/window management not provided?
As for window and input management it is a ton of work to abstract over
all possible platforms and there are already libraries like SDL or SFML or even
the platform itself which provide you with the functionality.
So instead of reinventing the wheel and trying to do everything the project tries
to be as independent and out of the users way as possible.
This means in practice a little bit more work on the users behalf but grants a
lot more freedom especially because the toolkit is designed to be embeddable.

The font management on the other hand is litte bit more tricky. In the beginning
the toolkit had some basic font handling but I removed it later. This is mainly
a question of if font handling should be part of a gui toolkit or not. As for a
framework the question would definitely be yes but for a toolkit library the
question is not as easy. In the end the project does not have font handling
since there are already a number of font handling libraries in existence or even the
platform (Xlib, Win32) itself already provides a solution.

## References
- [Tutorial from Jari Komppa about imgui libraries](http://www.johno.se/book/imgui.html)
- [Johannes 'johno' Norneby's article](http://iki.fi/sol/imgui/)
- [Casey Muratori's original introduction to imgui's](http:://mollyrocket.com/861?node=861)
- [Casey Muratori's imgui panel design(1/2)](http://mollyrocket.com/casey/stream_0019.html)
- [Casey Muratori's imgui panel design(2/2)](http://mollyrocket.com/casey/stream_0020.html)
- [Casey Muratori: Designing and Evaluation Reusable Components](http://mollyrocket.com/casey/stream_0028.html)
- [ImGui: The inspiration for this project](https://github.com/ocornut/imgui)
- [Nvidia's imgui toolkit](https://code.google.com/p/nvidia-widgets/)

# License
    (The MIT License)