shadertest.cpp

#include <Magnum/GL/Context.h>
#include <Magnum/Math/Color.h>
#include <Magnum/GL/Buffer.h>
#include <Magnum/GL/DefaultFramebuffer.h>
#include <Magnum/GL/Mesh.h>
#include <Magnum/Platform/Sdl2Application.h>
#include <Magnum/Shaders/FlatGL.h>

#include <iostream>

using namespace Magnum;

class MyApplication: public Platform::Application {
    public:
        explicit MyApplication(const Arguments& arguments);

    private:
        void drawEvent() override;

        GL::Buffer _buffer;
        GL::Mesh _mesh;
        Shaders::FlatGL2D _shader{NoCreate};
};

using namespace Math::Literals;
const float data[] = { -0.5f, -0.5f, 0.5f, -0.5f, 0.0f, 0.5f};

MyApplication::MyApplication(const Arguments& arguments): Platform::Application{arguments} {
    auto cs = Shaders::FlatGL2D::compile({}, 1, 1);
    // Uncommenting this makes it work as expected.
    //
    // while (!cs.isLinkFinished()) { std::cout << "."; std::cout.flush();}
    //
    std::cout << "constructor 1: " << cs.id() << " & " << cs.isLinkFinished() << std::endl;
    _shader = Shaders::FlatGL2D{std::move(cs)};
    std::cout << "constructor 2: " << _shader.id() << " & " << _shader.isLinkFinished() << std::endl;

    _shader.setColor(0x00ff00_rgbf);
    _buffer.setData(data, GL::BufferUsage::StaticDraw);
    _mesh.setPrimitive(GL::MeshPrimitive::Triangles)
        .setCount(3)
        .addVertexBuffer(_buffer, 0, 
            Shaders::FlatGL2D::Position{});
}

void MyApplication::drawEvent() {
    GL::defaultFramebuffer.clear(GL::FramebufferClear::Color);
    _mesh.draw(_shader);

    // This might print false on the first pass
    std::cout << "drawEvent: " << _shader.id() << " & " << _shader.isLinkFinished() << std::endl;

    swapBuffers();
}

MAGNUM_APPLICATION_MAIN(MyApplication)