Draft: Add shadow for Heroes Meeting dialog

[Furiiis]

Fixes: #7106

[Districh-ru]

Hi @Furiiis, your implementation is OK but there is one thing I've noticed.

The fheroes2::addGradientShadow() makes a shadow that is dropped from a solid object of some height (in example, buttons):

while all dialogs in the original game are considered as flat rectangles that are floating in some height over the game image:

So to be more consistent with the other in-game dialogs we can use the logic from:

fheroes2/src/fheroes2/gui/ui_window.cpp

Lines 348 to 370 in dbd923c

	// Render shadow at the left side of the window.
	int32_t offsetY = _windowArea.y + borderSize;
	ApplyTransform( _output, _totalArea.x, offsetY, borderSize, 1, 5 );
	++offsetY;
	ApplyTransform( _output, _totalArea.x, offsetY, 1, _windowArea.height - 2, 5 );
	ApplyTransform( _output, _totalArea.x + 1, offsetY, borderSize - 1, 1, 4 );
	++offsetY;
	ApplyTransform( _output, _totalArea.x + 1, offsetY, 1, _windowArea.height - 4, 4 );
	ApplyTransform( _output, _totalArea.x + 2, offsetY, borderSize - 2, 1, 3 );
	++offsetY;
	ApplyTransform( _output, _totalArea.x + 2, offsetY, 1, _windowArea.height - 6, 3 );
	ApplyTransform( _output, _totalArea.x + 3, offsetY, borderSize - 3, _windowArea.height - borderSize - 3, 2 );
	// Render shadow at the bottom side of the window.
	offsetY = _windowArea.y + _windowArea.height;
	const int32_t shadowBottomEdge = _windowArea.y + _totalArea.height;
	ApplyTransform( _output, _totalArea.x + 3, offsetY, _windowArea.width - 6, borderSize - 3, 2 );
	ApplyTransform( _output, _totalArea.x + 2, shadowBottomEdge - 3, _windowArea.width - 4, 1, 3 );
	ApplyTransform( _output, _totalArea.x + _windowArea.width - 3, offsetY, 1, borderSize - 3, 3 );
	ApplyTransform( _output, _totalArea.x + 1, shadowBottomEdge - 2, _windowArea.width - 2, 1, 4 );
	ApplyTransform( _output, _totalArea.x + _windowArea.width - 2, offsetY, 1, borderSize - 2, 4 );
	ApplyTransform( _output, _totalArea.x, shadowBottomEdge - 1, _windowArea.width, 1, 5 );
	ApplyTransform( _output, _totalArea.x + _windowArea.width - 1, offsetY, 1, borderSize - 1, 5 );

And put it to a new function in image.cpp (in example, we can name it addShadowForRectangularDialog()), use this new function here and in ui_window.cpp.

We could also make a new function more flexible to set the shadow offset like it is done for fheroes2::addGradientShadow(). And then we could also use the new function also to update the shadow for Battle::PopupDamageInfo and for the other such dialogs and pop-ups.

What do you think about such change?

[Furiiis]

Hi @Districh-ru,
I added a new parameter slopeEffect to fheroes2::addGradientShadow():

void addGradientShadow( const Sprite & in, Image & out, const Point & outPos, const Point & shadowOffset, const bool slopeEffect = true );

Now it can generate straight shadows, and we can replace this code:

// Render shadow at the left side of the window. 
 int32_t offsetY = _windowArea.y + borderSize; 
 ApplyTransform( _output, _totalArea.x, offsetY, borderSize, 1, 5 ); 
 ++offsetY; 
 ApplyTransform( _output, _totalArea.x, offsetY, 1, _windowArea.height - 2, 5 ); 
 ApplyTransform( _output, _totalArea.x + 1, offsetY, borderSize - 1, 1, 4 ); 
 ++offsetY; 
 ApplyTransform( _output, _totalArea.x + 1, offsetY, 1, _windowArea.height - 4, 4 ); 
 ApplyTransform( _output, _totalArea.x + 2, offsetY, borderSize - 2, 1, 3 ); 
 ++offsetY; 
 ...

with a simple call to fheroes2::addGradientShadow().

I didn't tested how it generates different shadow positions (left and top, top and right, right and bottom shadow lines). Of course such positions will never be used

[Districh-ru]

@Furiiis, unfortunately the updated code makes a sharp shadow:

while the original game dialog shadow is soft.
The fheroes2 engine (like the original game) has 4 values for shadow strength in the transform layer: from 5 (light) to 2 (strong).
The addGradientShadow() function increases the shadow strength in opposite direction relative to the shadowOffset parameter and also takes into account the "thickness" of the image in this direction for clamping the maximum shadow strength.
Sadly but this function cannot be easily updated to generate soft shadows for the "flat" objects.
That's why the code in ui_window.cpp was made.

The fast solution is to reuse it and make it a bit more flexible to generate such shadows for rectangular dialogs.
Later we can improve this solution to generate soft shadows for "flat" objects of any shape.