Triangle, but windowless

main.cpp

#include <Magnum/DebugTools/Screenshot.h>
#include <Magnum/GL/Buffer.h>
#include <Magnum/GL/Framebuffer.h>
#include <Magnum/GL/Mesh.h>
#include <Magnum/GL/Renderbuffer.h>
#include <Magnum/GL/RenderbufferFormat.h>
#ifdef MAGNUM_TARGET_HEADLESS
#include <Magnum/Platform/WindowlessEglApplication.h>
#elif defined(CORRADE_TARGET_IOS)
#include <Magnum/Platform/WindowlessIosApplication.h>
#elif defined(CORRADE_TARGET_APPLE)
#include <Magnum/Platform/WindowlessCglApplication.h>
#elif defined(CORRADE_TARGET_UNIX)
#if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_DESKTOP_GLES)
#include <Magnum/Platform/WindowlessGlxApplication.h>
#else
#include <Magnum/Platform/WindowlessEglApplication.h>
#endif
#elif defined(CORRADE_TARGET_WINDOWS)
#if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_DESKTOP_GLES)
#include <Magnum/Platform/WindowlessWglApplication.h>
#else
#include <Magnum/Platform/WindowlessWindowsEglApplication.h>
#endif
#else
#error no windowless application available on this platform
#endif
#include <Magnum/Shaders/VertexColor.h>

using namespace Magnum;

class MyApplication: public Platform::WindowlessApplication {
    public:
        using Platform::WindowlessApplication::WindowlessApplication;

        int exec() override;
};

int MyApplication::exec() {
    using namespace Math::Literals;

    struct TriangleVertex {
        Vector2 position;
        Color3 color;
    };
    const TriangleVertex data[]{
        {{-0.5f, -0.5f}, 0xff0000_rgbf},    /* Left vertex, red color */
        {{ 0.5f, -0.5f}, 0x00ff00_rgbf},    /* Right vertex, green color */
        {{ 0.0f,  0.5f}, 0x0000ff_rgbf}     /* Top vertex, blue color */
    };

    GL::Buffer buffer;
    buffer.setData(data);

    GL::Mesh mesh;
    mesh.setCount(3)
         .addVertexBuffer(std::move(buffer), 0,
            Shaders::VertexColor2D::Position{},
            Shaders::VertexColor2D::Color3{});

    GL::Renderbuffer renderbuffer;
    renderbuffer.setStorage(GL::RenderbufferFormat::RGBA8, {640, 480});
    GL::Framebuffer framebuffer{{{}, {640, 480}}};
    framebuffer.attachRenderbuffer(GL::Framebuffer::ColorAttachment{0}, renderbuffer)
        .clear(GL::FramebufferClear::Color)
        .bind();

    Shaders::VertexColor2D shader;
    mesh.draw(shader);

    if(DebugTools::screenshot(framebuffer, "triangle.png"))
         return 0;
    else {
        Error{} << "oh noes!";
        return 1;
    }
}

MAGNUM_WINDOWLESSAPPLICATION_MAIN(MyApplication)