[host] dxgi: add support for downsampling the capture before sending

This is an experimental & incomplete feature for those using
supersampling. Anything > 1200p will be downsampled by 50% before
copying out of the GPU to save on memory bandwidth.

Unfinished! Has issues with damage tracking and currently can not
be configured. Only dx11 has been tested at this point, everything
else will likely have problems/crash.

common/include/common/KVMFR.h

@@ -28,7 +28,7 @@
 #include "types.h"
 
 #define KVMFR_MAGIC   "KVMFR---"
-#define KVMFR_VERSION 18
+#define KVMFR_VERSION 19
 
 #define KVMFR_MAX_DAMAGE_RECTS 64
 
@@ -127,7 +127,8 @@ KVMFRCursor;
 enum
 {
   FRAME_FLAG_BLOCK_SCREENSAVER  = 0x1,
-  FRAME_FLAG_REQUEST_ACTIVATION = 0x2
+  FRAME_FLAG_REQUEST_ACTIVATION = 0x2,
+  FRAME_FLAG_TRUNCATED          = 0x4 // ivshmem was too small for the frame
 };
 
 typedef uint32_t KVMFRFrameFlags;
@@ -137,9 +138,10 @@ typedef struct KVMFRFrame
   uint32_t        formatVer;          // the frame format version number
   uint32_t        frameSerial;        // the unique frame number
   FrameType       type;               // the frame data type
-  uint32_t        width;              // the frame width
-  uint32_t        height;             // the frame height
-  uint32_t        realHeight;         // the real height if the frame was truncated due to low mem
+  uint32_t        screenWidth;        // the client's screen width
+  uint32_t        screenHeight;       // the client's screen height
+  uint32_t        frameWidth;         // the frame width
+  uint32_t        frameHeight;        // the frame height
   FrameRotation   rotation;           // the frame rotation
   uint32_t        stride;             // the row stride (zero if compressed data)
   uint32_t        pitch;              // the row pitch  (stride in bytes or the compressed frame size)