Monitor guide

Table of Contents

This guide introduces the monitor related functions of GLFW. For details on a specific function in this category, see the Monitor reference. There are also guides for the other areas of GLFW.

Monitor objects

A monitor object represents a currently connected monitor and is represented as a pointer to the opaque type GLFWmonitor. Monitor objects cannot be created or destroyed by the application and retain their addresses until the monitors they represent are disconnected or until the library is terminated.

Each monitor has a current video mode, a list of supported video modes, a virtual position, a human-readable name, an estimated physical size and a gamma ramp. One of the monitors is the primary monitor.

The virtual position of a monitor is in screen coordinates and, together with the current video mode, describes the viewports that the connected monitors provide into the virtual desktop that spans them.

To see how GLFW views your monitor setup and its available video modes, run the monitors test program.

Retrieving monitors

The primary monitor is returned by glfwGetPrimaryMonitor. It is the user's preferred monitor and is usually the one with global UI elements like task bar or menu bar.

You can retrieve all currently connected monitors with glfwGetMonitors. See the reference documentation for the lifetime of the returned array.

int count;
GLFWmonitor** monitors = glfwGetMonitors(&count);

The primary monitor is always the first monitor in the returned array, but other monitors may be moved to a different index when a monitor is connected or disconnected.

Monitor configuration changes

If you wish to be notified when a monitor is connected or disconnected, set a monitor callback.

glfwSetMonitorCallback(monitor_callback);

The callback function receives the handle for the monitor that has been connected or disconnected and the event that occurred.

void monitor_callback(GLFWmonitor* monitor, int event)
{
if (event == GLFW_CONNECTED)
{
// The monitor was connected
}
else if (event == GLFW_DISCONNECTED)
{
// The monitor was disconnected
}
}

If a monitor is disconnected, all windows that are full screen on it will be switched to windowed mode before the callback is called. Only glfwGetMonitorName and glfwGetMonitorUserPointer will return useful values for a disconnected monitor and only before the monitor callback returns.

Monitor properties

Each monitor has a current video mode, a list of supported video modes, a virtual position, a human-readable name, a user pointer, an estimated physical size and a gamma ramp.

Video modes

GLFW generally does a good job selecting a suitable video mode when you create a full screen window, change its video mode or make a windowed one full screen, but it is sometimes useful to know exactly which video modes are supported.

Video modes are represented as GLFWvidmode structures. You can get an array of the video modes supported by a monitor with glfwGetVideoModes. See the reference documentation for the lifetime of the returned array.

int count;
GLFWvidmode* modes = glfwGetVideoModes(monitor, &count);

To get the current video mode of a monitor call glfwGetVideoMode. See the reference documentation for the lifetime of the returned pointer.

const GLFWvidmode* mode = glfwGetVideoMode(monitor);

The resolution of a video mode is specified in screen coordinates, not pixels.

Physical size

The physical size of a monitor in millimetres, or an estimation of it, can be retrieved with glfwGetMonitorPhysicalSize. This has no relation to its current resolution, i.e. the width and height of its current video mode.

int width_mm, height_mm;
glfwGetMonitorPhysicalSize(monitor, &width_mm, &height_mm);

While this can be used to calculate the raw DPI of a monitor, this is often not useful. Instead use the monitor content scale and window content scale to scale your content.

Content scale

The content scale for a monitor can be retrieved with glfwGetMonitorContentScale.

float xscale, yscale;
glfwGetMonitorContentScale(monitor, &xscale, &yscale);

The content scale is the ratio between the current DPI and the platform's default DPI. If you scale all pixel dimensions by this scale then your content should appear at an appropriate size. This is especially important for text and any UI elements.

The content scale may depend on both the monitor resolution and pixel density and on user settings. It may be very different from the raw DPI calculated from the physical size and current resolution.

Virtual position

The position of the monitor on the virtual desktop, in screen coordinates, can be retrieved with glfwGetMonitorPos.

int xpos, ypos;
glfwGetMonitorPos(monitor, &xpos, &ypos);

Human-readable name

The human-readable, UTF-8 encoded name of a monitor is returned by glfwGetMonitorName. See the reference documentation for the lifetime of the returned string.

const char* name = glfwGetMonitorName(monitor);

Monitor names are not guaranteed to be unique. Two monitors of the same model and make may have the same name. Only the monitor handle is guaranteed to be unique, and only until that monitor is disconnected.

User pointer

Each monitor has a user pointer that can be set with glfwSetMonitorUserPointer and queried with glfwGetMonitorUserPointer. This can be used for any purpose you need and will not be modified by GLFW. The value will be kept until the monitor is disconnected or until the library is terminated.

The initial value of the pointer is NULL.

Gamma ramp

The gamma ramp of a monitor can be set with glfwSetGammaRamp, which accepts a monitor handle and a pointer to a GLFWgammaramp structure.

unsigned short red[256], green[256], blue[256];
ramp.size = 256;
ramp.red = red;
ramp.green = green;
ramp.blue = blue;
for (i = 0; i < ramp.size; i++)
{
// Fill out gamma ramp arrays as desired
}
glfwSetGammaRamp(monitor, &ramp);

The gamma ramp data is copied before the function returns, so there is no need to keep it around once the ramp has been set.

It is recommended that your gamma ramp have the same size as the current gamma ramp for that monitor.

The current gamma ramp for a monitor is returned by glfwGetGammaRamp. See the reference documentation for the lifetime of the returned structure.

const GLFWgammaramp* ramp = glfwGetGammaRamp(monitor);

If you wish to set a regular gamma ramp, you can have GLFW calculate it for you from the desired exponent with glfwSetGamma, which in turn calls glfwSetGammaRamp with the resulting ramp.

glfwSetGamma(monitor, 1.0);

To experiment with gamma correction via the glfwSetGamma function, run the gamma test program.

Note
The software controlled gamma ramp is applied in addition to the hardware gamma correction, which today is usually an approximation of sRGB gamma. This means that setting a perfectly linear ramp, or gamma 1.0, will produce the default (usually sRGB-like) behavior.