add C module to get the Windows display information

src/displayinfo.c

@@ -0,0 +1,51 @@
+/*
+ * Author: Josh Holtrop
+ * This Windows-specific module will get the screen size
+ * and return the number of monitors present.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <windows.h>
+
+void GetDisplaySize(int * width, int * height, int * num_monitors)
+{
+    int w = 0;
+    int h = 0;
+    int n = 0;
+
+    /* loop through the display devices to get their dimensions */
+    for (int i = 0; i < 10; i++)
+    {
+        DISPLAY_DEVICE dev;
+        dev.cb = sizeof(DISPLAY_DEVICE);
+        if (!EnumDisplayDevices(NULL, i, &dev, 0))
+            break;
+        /* we only want real display devices to matter */
+        if ((strcmp(dev.DeviceID, "") != 0) && (dev.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP))
+        {
+            HDC hdc = CreateDC(TEXT("DISPLAY"), dev.DeviceString, NULL, NULL);
+            if (hdc != NULL)
+            {
+                n++;
+                w += GetDeviceCaps(hdc, HORZRES);
+                int thisHeight = GetDeviceCaps(hdc, VERTRES);
+                /* assume monitors are all horizontally aligned */
+                if (thisHeight > h)
+                    h = thisHeight;
+            }
+        }
+    }
+
+    /* only update width and height if we have valid data */
+    if (w != 0 && h != 0)
+    {
+        if (width != NULL)
+            *width = w;
+        if (height != NULL)
+            *height = h;
+        if (num_monitors != NULL)
+            *num_monitors = n;
+    }
+}