# How to request redraw of Cinder window

**URL:** <https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690>\
**Category:** Using Cinder\
**Created:** [August 11, 2020, 9:59am UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690 "2020-08-11T09:59:55Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![totalgee](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.libcinder.org/totalgee/32/274_2.png) [@totalgee](https://discourse.libcinder.org/u/totalgee)\
**Post date:** [August 11, 2020, 9:59am UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690/1 "2020-08-11T09:59:55Z")

</div>

Hi there. I’d like to have a UI Cinder app (e.g. using ImGui) that is set to a slow (ideally 0 😉 ) refresh rate, e.g.

```auto
    app::setFrameRate(4);

```

Then, I’d like certain behaviours (like mouse click or drag, or when OSC messages arrive) to request window refreshes, so the response is quick in those cases. I don’t see an obvious (or cross-platform) way to request an update/redraw of the window. I thought maybe I could “emit” a request redraw message somehow in a generic way, but this isn’t (for example) what `emitDraw()` does, from what I can tell.

I’ve managed to find platform-specific workarounds, but was very curious if there’s a Cinder “built-in” way to do this nicely. Here’s my version, for Windows at least:

```auto
namespace {
    void redraw(app::WindowRef const& win)
    {
#if defined( CINDER_MSW )
        HWND hwnd = static_cast<HWND>(win->getNative());
        ::RedrawWindow(hwnd, NULL, NULL, RDW_INVALIDATE | RDW_UPDATENOW);
#elif defined( CINDER_MAC )
        // NSView ...
#elif defined( CINDER_LINUX )
        // ...
#endif // CINDER_MSW
    }
}

void MyApp::mouseDown(app::MouseEvent event)
{
    ::redraw(event.getWindow());
}

void MyApp::keyDown(app::KeyEvent event)
{
    ::redraw(event.getWindow());
}

```

Thanks,  
Glen.

---

<div class="post-metadata">

**Author:** ![paul.houx](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.libcinder.org/paul.houx/32/31_2.png) [@paul.houx](https://discourse.libcinder.org/u/paul.houx)\
**Post date:** [August 15, 2020, 7:01pm UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690/2 "2020-08-15T19:01:09Z")

</div>

Hi Glen,

it could be as simple as having a `boolean` that controls whether the window should redraw or not:

```auto
class YourApp : public App {
  public:
    void draw() override;
    void mouseDown( MouseEvent event ) override;
    void redraw();

  private:
    boolean mShouldRedraw = true;
};

void YourApp::draw()
{
    if( mShouldRedraw ) {
        redraw();

        mShouldRedraw = false;
    }
}

void YourApp::mouseDown( MouseEvent event )
{
    mShouldRedraw = true;
}

void YourApp::redraw()
{
    // Clear the current contents.
    gl::clear();

    // ...draw your UI...
}

```

Note that as long as you don’t clear the window, the contents will remain visible.

-Paul

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<div class="post-metadata">

**Author:** ![totalgee](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.libcinder.org/totalgee/32/274_2.png) [@totalgee](https://discourse.libcinder.org/u/totalgee)\
**Post date:** [August 16, 2020, 4:02pm UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690/3 "2020-08-16T16:02:37Z")

</div>

Thanks, but I don’t see how that could work; won’t we just get flipping between the last two framebuffers in that case (Cinder will still do a “swap” after calling `draw()`)… And anyhow, the behaviour should be system-dependent, because some systems may not maintain valid buffers when drawing with another window (partly) on top, or may copy and invalidate the back buffer after “swapping”). At least that’s how things used to work in the “old days” – there might be a trick I’m missing to get it to work. (-;

Do you have an example? I made one (basically what you suggested above), and indeed (on Windows) I get what I expected – flickering between the previous and next buffers.

Thanks,  
Glen.

---

<div class="post-metadata">

**Author:** ![totalgee](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.libcinder.org/totalgee/32/274_2.png) [@totalgee](https://discourse.libcinder.org/u/totalgee)\
**Post date:** [August 16, 2020, 4:04pm UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690/4 "2020-08-16T16:04:49Z")

</div>

Here’s a complete example that (on Windows) shows the flickering between two different buffers when simply skipping drawing in the `draw()` method as you suggest…

```auto
#include "cinder/app/App.h"
#include "cinder/app/RendererGl.h"
#include "cinder/gl/gl.h"

using namespace ci;
using namespace ci::app;

class YourApp : public App {
public:
    void draw() override;
    void mouseDown(MouseEvent event) override;
    void redraw();

private:
    bool mShouldRedraw = true;
    Font mFont{ "Arial", 36 };
};

void YourApp::draw()
{
    if (mShouldRedraw) {
        redraw();
    }
}

void YourApp::mouseDown(MouseEvent event)
{
    mShouldRedraw = true;
}

void YourApp::redraw()
{
    mShouldRedraw = false;

    // Clear the current contents.
    gl::clear(Color::black());

    static uint32_t drawNum = 0;
    auto const sz = getWindowSize();
    gl::drawStringCentered(std::to_string(app::getElapsedFrames()),
        vec2(20 + (drawNum % 2) * (sz.x - 40), 20 + (drawNum / 2) * (sz.y - 60)),
        Color(0.6f, 0.9f, 0.2f),
        mFont);
    drawNum = (drawNum + 1) % 4;
    // ...draw your UI...
}

CINDER_APP(YourApp, app::RendererGl, [](app::App::Settings* settings) {
    settings->setWindowSize(320, 240);
    settings->setWindowPos(40, 40);
    settings->setFrameRate(30);
    })

```

---

<div class="post-metadata">

**Author:** ![Svintaj](https://avatars.discourse-cdn.com/v4/letter/s/fbc32d/32.png) [@Svintaj](https://discourse.libcinder.org/u/Svintaj)\
**Post date:** [June 21, 2021, 1:59pm UTC](https://discourse.libcinder.org/t/how-to-request-redraw-of-cinder-window/1690/5 "2021-06-21T13:59:57Z")

</div>

I would also like to request several redraws to keep animations playing while moving or touching the border of the main window. I guess I could just fire the update() and draw() functions myself. But how can I get a ~‘windowIsMoving’ event to act upon, is it possible? 🤔

Or is there another way to achieve this in Cinder, shall I enable or disable something? 🤷‍♂️

(I have also noticed that buffer-flickering when prevent drawing, for me it goes away when I maximize the window though. Still wondering what’s going on and how to avoid that flickering? I’m also on Windows.)