py-imgui-redux

PyImGui

DearImGui wrapper for python made with PyBind11

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Read below for adjustments made to the standard APIs. Otherwise, all documentation from the original libraries remains 100% valid. Check out the examples folder for some concrete code.

Install

Install the latest version with pip

pip install py-imgui-redux

Modules:

imgui - Core DearImGUI
imgui.implot - ImPlot library
imgui.imnodes - ImNodes library
imgui.glfw - GLFW Bindings

Backends:

This module only uses the GFLW+OpenGL3 backend. imgui.glfw provides full access to GLFW's API, see below for it's adjustments

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API Adjustments

I am writing this library with the primary goal of keeping the original Dear ImGui functional API as intact as possible. This is because:

1. I want to keep all C++ examples and documentation as relevant as possible since I am lazy and don't want to rewrite everything.
2. I have a love-hate relationship with snake-case.

However, there are some minor compromises that have to be made in order to make this happen, primarily in the case of pointers and lists.

Pointers

Take for instance the function:

bool DragIntRange2(const char* label, int* v_current_min, int* v_current_max, /* other args... */);

1. This function returns true if the state changed
2. v_current_min and v_current_max are pointers to state, and will be read and updated if a change is made

Typical C++ usage

int min = 0;
int max = 5;
// Code ...
if(imgui::DragIntRange2("Label", &min, &max))
{
    // Code that happens if a change was made
}

Python, however, will not let you pass an integer by reference normally, let alone across the C API. Therefore, the py-imgui-redux method of accomplishing this:

min_val = imgui.IntRef(0)
max_val = imgui.IntRef(5)
# Code ...
if imgui.DragIntRange2("Label", min_val, max_val):
    # Code that happens if a change was made
    pass

These are thin wrappers around a single value.

imgui.IntRef
imgui.FloatRef
imgui.BoolRef
# The value can be accessed like so
myNum = imgui.IntRef(25)
myNum.val += 2

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Lists

Take for instance the function

bool DragInt3(const char* label, int v[3], /* args ... */);

A standard python list is stored sequentially in memory, but the raw values themselves are wrapped in a python object. Therefore, we cannot easily iterate over just the ints/floats, let alone get a pointer to give to ImGui. PyBind11 will happily take a python list and turn it into a vector for us, but in doing so requires making a copy of the list (not ideal for large lists)

This is solved in one of two ways.

Method 1: py-imgui-redux Wrappers

vals = imgui.IntList([0, 5, 10])
if imgui.DragInt3("Label", vals):
    # updating code
    pass

These are thin wrappers around a C++ vector. They have standard python list access functions and iteration capabilities.

imgui.IntList
imgui.FloatList
imgui.DoubleList

x = imgui.IntList()
x.append(25)
x.append(36)

print(len(x))

for val in x:
    print(x)

x[0] = 12

See their docs for more information and all functions.

Functions that mutate the data, such as vanilla ImGui widgets will use this method.

Method 2: Numpy Arrays

import numpy as np
xs = np.array([0, 5, 10])
ys = np.array([0, 5, 10])
# Code...
implot.PlotScatter("Scatter", xs, ys, len(xs))

The implot submodule uses these, as they prevent the need to copy potentially large arrays, and implot functions will not need to change the data as it reads it. Numpy is also easier to use for data manipulations as is typical with plotting.

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Thirdly, references to strings are handled similarily to lists (it's actually a subclass of the List wrappers).

Take for instance the function

bool InputText(const char* label, char* buf, size_t buf_size, /* args ... */);

Which takes a pointer to the IO buffer, and also and argument for its size.

In Python:

myStr = imgui.StrRef("This is a string", maxSize=20)
# Code ...
if imgui.InputText("Label", myStr):
    # code if the text changes
    pass

Notice that you don't need to pass the size, this is baked into the StrRef. Note: maxSize automatically takes into account string terminators, i.e. maxSize=20 means your string can hold 20 chars.

To change the maxSize:

myStr.resize(25)

Changing the size lower will drop any extra chars.

To get your string back

# make a copy
x = str(myStr)
# or
x = myStr.copy()

# get a temporary/unsafe pointer
# useful for printing large strings without copying
# only use said pointer while the object exists
# lest ye summon the dreaded seg-fault
print(myStr.view())

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Images

Loading images for rendering is simple

import imgui

texture = imgui.LoadTextureFile("myImage.jpg")
imgui.Image(texture, imgui.ImVec2(texture.width, texture.height))
# ...
# Eventually
glfw.UnloadTexture(texture)
# texture can no longer be used without a call to LoadTexture

Image file loading is handled via stb_image and supports various common file formats. Alternatively, if you wish to do some manual image processing, you can use PILLOW or OpenCV (or any other image processing library... probably)

Important Note: LoadTexture and LoadTextureFile can only be called after both imgui and glfw have been initialized otherwise openGL will segfault

OpenCV Example

import imgui
import cv2

image = cv2.imread("myImage.jpg", cv2.IMREAD_UNCHANGED)
# cv2.IMREAD_UNCHANGED is important for files with alpha

# Have to convert the colors first
image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
# If your image has alpha: cv2.COLOR_GBRA2RGBA

texture = imgui.LoadTexture(image.tobytes(),
                            image.shape[1],
                            image.shape[0],
                            image.shape[2])

PILLOW Example

import imgui
from PIL import Image

image = Image.open("myImage.jpg")
texture = imgui.LoadTexture(image.tobytes(),
                            image.size[0],
                            image.size[1],
                            len(image.getbands()))

GLFW API Adjustments

This wrapper aims to be as close to the original API as possible. Exceptions:

• Functions have lost the glfw prefix as this is already in the module name
• Functions that returned pointers to arrays now return list-like objects
• Functions that took pointers to output variables as arguments now return tuples

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Build Dependencies

Debian/apt

libx11-dev libxrandr-dev libxinerama-dev libxcursor-dev libxi-dev libgl-dev

Fedora/yum

libXrandr-devel libXinerama-devel libXcursor-devel libXi-devel mesa-libGL-devel