nikolausrauch / 2d-viewer

A 2D Viewer/Interface Library (OpenGL2) for drawing primitives / ui / plots

2D Viewer

This repository contains a small viewer library (C++ and OpenGL2) encapsulating window, and input handling, primitive, and graphical user interface (ImGui/ImPlot) rendering.
I wrote it originally for visualizing physically based simulation approaches (mass-spring systems, rigid-bodies, SPH, etc.). Over the years it has been used for teaching purposes, e.g. practical assignments, at my university.

It has the following in-source external dependencies: glfw, glm, imgui, implot, stb_image.

Minimal Example

The Viewer class provides the interface to configure window/render behaviour and to register callbacks for the following events:

• init: is called after the opengl context is initialized
• shutdown: is called right before the opengl context is destroyed
• key: triggered if a key is pressed or released
• mouseButton: triggered if a mouse button is pressed or released
• update: called before rendering (once per frame)
• draw: used to submit render calls (points, lines, quads, triangles, circles, ...)
• gui: used to draw/respond to user-interface via ImGui and ImPlot

    Viewer viewer;
    viewer.mWindow.title = "Example";
    viewer.mWindow.width = 1280;
    viewer.mWindow.height = 720;
    viewer.mWindow.vsync = true;
    viewer.mWindow.mHDPI = false;

    /* install callback functions for events */
    viewer.onUpdate([](Window& window, double dt){ });
    viewer.onDraw([](Window& window, double dt){ });
    viewer.onGui([](Window& window, double dt){ });
    viewer.onMouseButton([](Window& window, Mouse& mouse, int button, int mod, bool press){ });
    viewer.onKey([](Window& window, Keyboard& keyboard, int key, int mod, bool press){ });
 
    /* start viewer (OpenGL context is created, use drawcommands and loading functions only in callbacks) */
    viewer.run();

See demo/demo.cpp for a detailed overview of the libraries functionalities.

Examples

Assignments for a physically-based simulation course (mass-spring systems, rigid-body simulation, stable fluid, finite element method).

2d-viewer's Issues

Memory Corruption on MacOS

In your demo, there's a code passage at

2D-viewer/demo/demo.cpp

Lines 71 to 77 in 9bb5068

	viewer.drawCircles(circles.begin(), circles.end(), [](auto& c, auto& pos, auto& radius, auto& color)
	{
	pos = c.first;
	radius = c.second;
	color = {0.0, 1.0, 0.0, 1.0};
	return true;
	});

When executed on a MacBook (with an M1 processor), it leads to the following error:

demo(55959,0x1dc8fd000) malloc: Incorrect checksum for freed object 0x14a608310: probably modified after being freed.
Corrupt value: 0x343bbd2e3f800000
demo(55959,0x1dc8fd000) malloc: *** set a breakpoint in malloc_error_break to debug
[1]    55959 abort      ./bin/demo

It appears that the initialization of the new vector (vertices) in this function is broken on MacOS. Specifically, referring to

2D-viewer/viewer/viewer.inl

Lines 50 to 58 in 9bb5068

	std::vector<glm::vec2> vertices(mRender.circleVertices);
	for(unsigned int i = 0; i <= mRender.circleVertices; i++)
	{
	vertices[i] =
	{
	radius * glm::cos(2.0*glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices),
	radius * glm::sin(2.0*glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices)
	};
	}

There could be two (or more) ways (for now) to fix this:

You could do something like:

#ifndef __APPLE__
std::vector<glm::vec2> vertices(mRender.circleVertices);
for (unsigned int i = 0; i <= mRender.circleVertices; i++) {
    vertices[i] = {
        radius * glm::cos(2.0 * glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices),
        radius * glm::sin(2.0 * glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices)};
}
#endif

...

for (unsigned int i = 0; i <= mRender.circleVertices; i++) {
#ifdef __APPLE__
    glVertex2f(position.x + radius * radius * glm::cos(2.0 * glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices),
                       position.y + radius * radius * glm::sin(2.0 * glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices));
#else
    glVertex2f(position.x + radius * vertices[i].x,
                       position.y + radius * vertices[i].y);
#endif
}

Or, without the #ifdef:

...
for (unsigned int i = 0; i <= mRender.circleVertices; i++) {
    const float angle = 2.0 * glm::pi<float>() * static_cast<float>(i) / mRender.circleVertices;  // For readability purposes
    glVertex2f(position.x + radius * radius * glm::cos(angle),
                       position.y + radius * radius * glm::sin(angle));
}

As you mentioned, you're not exactly sure why this happens, but with these changes, it wouldn't occur anymore. Additionally, you questioned why the vertices array is used in the first place, since, from your understanding, these vertices are only used once.