Moved open and close of display to the 'grab' method, solving resolution switches.

Added doxygen comments to the dispmanx header.

libsrc/dispmanx-grabber/DispmanxFrameGrabber.cpp

@@ -2,41 +2,47 @@
 #include "DispmanxFrameGrabber.h"
 
 DispmanxFrameGrabber::DispmanxFrameGrabber(const unsigned width, const unsigned height) :
-	_display(0),
-	_resource(0),
+	_vc_display(0),
+	_vc_resource(0),
 	_width(width),
 	_height(height)
 {
 	// Initiase BCM
 	bcm_host_init();
 
-	// Open the connection to the display
-	_display = vc_dispmanx_display_open(0);
-	int ret = vc_dispmanx_display_get_info(_display, &_info);
-	// Make the compiler (in release mode) happy by 'using' ret
-	(void)ret;
-	assert(ret == 0);
+	{
+		// Check if the display can be opened and display the current resolution
+		// Open the connection to the display
+		_vc_display = vc_dispmanx_display_open(0);
+		assert(_vc_display > 0);
+
+		// Obtain the display information
+		DISPMANX_MODEINFO_T vc_info;
+		int result = vc_dispmanx_display_get_info(_vc_display, &vc_info);
+		assert(result == 0);
+		std::cout << "Display opened with resolution: " << vc_info.width << "x" << vc_info.height << std::endl;
+
+		// Close the displaye
+		vc_dispmanx_display_close(_vc_display);
+	}
 
 	// Create the resources for capturing image
-	_resource = vc_dispmanx_resource_create(
+	uint32_t vc_nativeImageHandle;
+	_vc_resource = vc_dispmanx_resource_create(
 			VC_IMAGE_RGB888,
 			width,
 			height,
-			&_vc_image_ptr);
-	assert(_resource);
+			&vc_nativeImageHandle);
+	assert(_vc_resource);
 
 	// Define the capture rectangle with the same size
 	vc_dispmanx_rect_set(&_rectangle, 0, 0, width, height);
-	_pitch = width * 3;
 }
 
 DispmanxFrameGrabber::~DispmanxFrameGrabber()
 {
 	// Clean up resources
-	vc_dispmanx_resource_delete(_resource);
-
-	// Close the displaye
-	vc_dispmanx_display_close(_display);
+	vc_dispmanx_resource_delete(_vc_resource);
 
 	// De-init BCM
 	bcm_host_deinit();
@@ -47,10 +53,17 @@ void DispmanxFrameGrabber::grabFrame(RgbImage& image)
 	// Sanity check of the given image size
 	assert(image.width() == _width && image.height() == _height);
 
-	void* image_ptr = image.memptr();
+	// Open the connection to the display
+	_vc_display = vc_dispmanx_display_open(0);
 
-	// Create the snapshot
-	vc_dispmanx_snapshot(_display, _resource, VC_IMAGE_ROT0);
-	// Read the snapshot into the memory (incl down-scaling)
-	vc_dispmanx_resource_read_data(_resource, &_rectangle, image_ptr, _pitch);
+	// Create the snapshot (incl down-scaling)
+	vc_dispmanx_snapshot(_vc_display, _vc_resource, VC_IMAGE_ROT0);
+
+	// Read the snapshot into the memory
+	void* image_ptr = image.memptr();
+	const unsigned destPitch = _width * 3;
+	vc_dispmanx_resource_read_data(_vc_resource, &_rectangle, image_ptr, destPitch);
+
+	// Close the displaye
+	vc_dispmanx_display_close(_vc_display);
 }

libsrc/dispmanx-grabber/DispmanxFrameGrabber.h

@@ -11,26 +11,43 @@
 #include <utils/RgbImage.h>
 
 ///
-/// The DispmanxFrameGrabber grabs
+/// The DispmanxFrameGrabber is used for creating snapshots of the display (screenshots) with a
+/// downsized and scaled resolution.
 ///
 class DispmanxFrameGrabber
 {
 public:
+	///
+	/// Construct a DispmanxFrameGrabber that will capture snapshots with specified dimensions.
+	///
+	/// @param[in] width  The width of the captured screenshot
+	/// @param[in] height The heigth of the captured screenshot
+	///
 	DispmanxFrameGrabber(const unsigned width, const unsigned height);
 	~DispmanxFrameGrabber();
 
+	///
+	/// Captures a single snapshot of the display and writes the data to the given image. The
+	/// provided image should have the same dimensions as the configured values (_width and
+	/// _height)
+	///
+	/// @param[out] image  The snapped screenshot (should be initialized with correct width and
+	/// height)
+	///
 	void grabFrame(RgbImage& image);
 
 private:
-	DISPMANX_DISPLAY_HANDLE_T _display;
-	DISPMANX_MODEINFO_T _info;
+	/// Handle to the display that is being captured
+	DISPMANX_DISPLAY_HANDLE_T _vc_display;
 
-	DISPMANX_RESOURCE_HANDLE_T _resource;
-
-	uint32_t _vc_image_ptr;
+	/// Handle to the resource for storing the captured snapshot
+	DISPMANX_RESOURCE_HANDLE_T _vc_resource;
 
+	/// Rectangle of the captured resource that is transfered to user space
 	VC_RECT_T _rectangle;
+
+	/// With of the captured snapshot [pixels]
 	unsigned _width;
+	/// Height of the captured snapshot [pixels]
 	unsigned _height;
-	uint32_t _pitch;
 };