Functions for using screen positions in GUI component gui.set_screen_pos()

[AGulev]

Is your feature request related to a problem? Please describe (REQUIRED):
For manipulations between game world and gui or between different gui components the engine should have API to convert cordinates using some universal cordinates system.
At the moment we use screen coordinates as such universal coordinates we may use for conversion.

Describe the solution you'd like (REQUIRED):
The engine has functions to get screen cordinates, but there are no functions in gui to use them.
I think the engine should have :
gui.set_screen_pos()
and
local pos = gui.convert_screen_pos_to_node_pos(node, screen_pos) (it's hard to find clear and short name here, pls suggest your variants).

Describe alternatives you've considered (REQUIRED):
I implemented these functions in the native extension, but I think it should be part of the gui.* API.
https://github.com/AGulev/set_screen_position

[AGulev]

defold/engine/gui/src/gui.cpp

Lines 4254 to 4312 in b240830

	if (keep_scene_transform) {
	Matrix4 node_m;
	Matrix4 parent_m;
	Vector4 reference_scale;
	Vector4 adjust_scale;
	Vector4 offset(0.0f);
	// Calculate the nodes current scene transform
	CalculateNodeTransform(scene, n, CalculateNodeTransformFlags(), node_m);
	// Calculate the new parents scene transform
	// We also need to calculate values relative to adjustments and offset
	// corresponding to the values that would be used in AdjustPosScale (see reasoning below).
	if (parent_node != 0x0)
	{
	CalculateNodeTransform(scene, parent_node, CalculateNodeTransformFlags(), parent_m);
	reference_scale = parent_node->m_Node.m_LocalAdjustScale;
	adjust_scale = ApplyAdjustOnReferenceScale(reference_scale, n->m_Node.m_AdjustMode);
	} else {
	reference_scale = CalculateReferenceScale(scene, 0x0);
	adjust_scale = ApplyAdjustOnReferenceScale(reference_scale, n->m_Node.m_AdjustMode);
	parent_m = Matrix4::scale(adjust_scale.getXYZ());
	Vector4 parent_dims = Vector4((float) scene->m_Width, (float) scene->m_Height, 0.0f, 1.0f);
	Vector4 adjusted_dims = mulPerElem(parent_dims, adjust_scale);
	Vector4 ref_size = Vector4((float) scene->m_Context->m_PhysicalWidth, (float) scene->m_Context->m_PhysicalHeight, 0.0f, 1.0f);
	offset = (ref_size - adjusted_dims) * 0.5f;
	}
	// We calculate a new position that will be the relative position once
	// the node has been childed to the new parent.
	Vector3 position = node_m.getCol3().getXYZ() - parent_m.getCol3().getXYZ();
	// We need to perform the inverse of what AdjustPosScale will do to counteract when
	// it will be applied during next call to CalculateNodeTransform.
	// See AdjustPosScale for comparison on the steps being performed/inversed.
	if (n->m_Node.m_XAnchor == XANCHOR_LEFT || n->m_Node.m_XAnchor == XANCHOR_RIGHT) {
	offset.setX(0.0f);
	}
	if (n->m_Node.m_YAnchor == YANCHOR_TOP || n->m_Node.m_YAnchor == YANCHOR_BOTTOM) {
	offset.setY(0.0f);
	}
	Vector3 scaled_position = position - offset.getXYZ();
	position = mulPerElem(recipPerElem(adjust_scale.getXYZ()), scaled_position);
	if (n->m_Node.m_XAnchor == dmGui::XANCHOR_LEFT || n->m_Node.m_XAnchor == dmGui::XANCHOR_RIGHT) {
	position.setX(scaled_position.getX() / reference_scale.getX());
	}
	if (n->m_Node.m_YAnchor == dmGui::YANCHOR_BOTTOM || n->m_Node.m_YAnchor == dmGui::YANCHOR_TOP) {
	position.setY(scaled_position.getY() / reference_scale.getY());
	}
	n->m_Node.m_Properties[dmGui::PROPERTY_POSITION] = Vector4(position, 1.0f);
	n->m_Node.m_DirtyLocal = 1;
	}

[Sublustris]

Very useful feature. Sometime it is very frustrating when you need to synchronize positions of nodes in several GUIs. Aligning them according to screen coordinates is a key to this problem and gui.set_screen_pos() would be very helpful.

[AGulev]

Design: https://docs.google.com/document/d/1kQZi7BOKdWcNsnkA1_hzkjLUPmhl64wvLANuEE6tzU8/edit#heading=h.umz08cc31mce