correct placement and box model

src/main.c3

@@ -53,15 +53,15 @@ fn int main(String[] args)
 		// main div, fill the whole window
 		ctx.div_begin("main", ugui::Rect{.w=ctx.width/2})!!;
 		{|
-			ctx.layout_set_column()!!;
+			ctx.layout_set_row()!!;
 			if (ctx.button("button0", ugui::Rect{0,0,30,30})!!.mouse_press) {
 				io::printn("press button0");
 			}
-			ctx.layout_next_column()!!;
+			//ctx.layout_next_column()!!;
 			if (ctx.button("button1", ugui::Rect{0,0,30,30})!!.mouse_press) {
 				io::printn("press button1");
 			}
-			ctx.layout_next_column()!!;
+			//ctx.layout_next_column()!!;
 			if (ctx.button("button2", ugui::Rect{0,0,30,30})!!.mouse_release) {
 				io::printn("release button2");
 			}

src/ugui_data.c3

@@ -52,6 +52,11 @@ enum DivLayout {
 // div element
 struct Div {
 	DivLayout layout;
+	bool can_scroll_x;
+	bool can_scroll_y;
+	isz vertical_scroll_bar;
+	isz horizontal_scroll_bar;
+	Rect children_bounds;
 	Point origin_r, origin_c;
 	Color color_bg;
 }
@@ -208,3 +213,9 @@ macro rect_intersection(Rect a, Rect b)
         .h = (short)min(a.y+a.h, b.y+b.h) - (short)max(a.y, b.y),
     };
 }
+
+// rect intersection not null
+macro rect_collision(Rect a, Rect b)
+{
+    return !(a.x > b.x+b.w || a.x+a.w < b.x || a.y > b.y+b.h || a.y+a.h < b.y);
+}

src/ugui_div.c3

@@ -17,6 +17,9 @@ fn void! Ctx.div_begin(&ctx, String label, Rect size)
 	if (c_elem.flags.is_new || parent.flags.updated) {
 		// 2. layout the element
 		c_elem.bounds = ctx.position_element(parent, size);
+		if (c_elem.flags.is_new) {
+			c_elem.div.children_bounds = c_elem.bounds;
+		}
 
 		// 3. Mark the element as updated
 		c_elem.flags.updated = true;
@@ -28,6 +31,10 @@ fn void! Ctx.div_begin(&ctx, String label, Rect size)
 		};
 		c_elem.div.color_bg = uint_to_rgba(0xff0000ff);
 		c_elem.div.origin_r = c_elem.div.origin_c;
+		c_elem.div.can_scroll_x = false;
+		c_elem.div.can_scroll_y = false;
+		c_elem.div.vertical_scroll_bar = -1;
+		c_elem.div.horizontal_scroll_bar = -1;
 	}
 
 	// Add the background to the draw stack

src/ugui_impl.c3

@@ -32,6 +32,12 @@ macro Ctx.get_elem_by_label(&ctx, String label)
     return ctx.cache.search(id);
 }
 
+macro Ctx.get_elem_by_tree_idx(&ctx, isz idx) @private
+{
+    Id id = ctx.tree.get(ctx.active_div)!;
+	return ctx.cache.search(id);
+}
+
 fn void! Ctx.init(&ctx)
 {
 	ctx.tree.init(MAX_ELEMENTS)!;

src/ugui_layout.c3

@@ -75,9 +75,12 @@ fn void! Ctx.layout_next_column(&ctx)
 }
 
 // position the rectangle inside the parent according to the layout
+// parent: parent div
+// rect: the requested size
+// style: apply style
 fn Rect Ctx.position_element(&ctx, Elem *parent, Rect rect, bool style = false)
 {
-	Rect  bounds;
+	Rect  placement;
 	Point origin;
 
 	// 1. Select the right origin
@@ -91,49 +94,65 @@ fn Rect Ctx.position_element(&ctx, Elem *parent, Rect rect, bool style = false)
 		// Error
 	}
 
-	// 2. Position the rect
-	bounds.x = (short)max(origin.x + rect.x, 0);
-	bounds.y = (short)max(origin.y + rect.y, 0);
+	// the bottom-right border of the element box
+	Point pl_corner;
 
-	// 3. Calculate width & height
-	// FIXME: account for origin offset!!
-	bounds.w = rect.w > 0 ? rect.w : parent.bounds.w;
-	bounds.h = rect.h > 0 ? rect.h : parent.bounds.h;
+	// 2. Calculate the placement
+	placement.x = (short)max(origin.x + rect.x, 0);
+	placement.y = (short)max(origin.y + rect.y, 0);
+	placement.w = rect.w > 0 ? rect.w : parent.bounds.w - (placement.x - parent.bounds.x);
+	placement.h = rect.h > 0 ? rect.h : parent.bounds.h - (placement.y - parent.bounds.y);
 
-	// 4. Update the origins of the parent
+	pl_corner.x = placement.x + placement.w;
+	pl_corner.y = placement.y + placement.h;
+
+	// 2.1 apply style, css box model
+	if (style) {
+	    Rect margin = ctx.style.margin;
+	    Rect border = ctx.style.border;
+		Rect padding = ctx.style.padding;
+
+		placement.x += margin.x;
+		placement.y += margin.y;
+		if (rect.w != 0) { placement.w += margin.x+margin.w + padding.x+padding.w; }
+		if (rect.h != 0) { placement.h += margin.y+margin.h + padding.y+padding.h; }
+
+		pl_corner.x = placement.x + placement.w + margin.w;
+		pl_corner.y = placement.y + placement.h + margin.h;
+	}
+
+	// 3. Update the origins of the parent
 	parent.div.origin_r = Point{
-	    .x = bounds.x + bounds.w,
-	    .y = bounds.y,
+	    .x = pl_corner.x,
+	    .y = origin.y,
 	};
 	parent.div.origin_c = Point{
-	    .x = bounds.x,
-	    .y = bounds.y + bounds.h,
+	    .x = origin.x,
+	    .y = pl_corner.y,
 	};
 
-	// if using the style then apply margins
-	// FIXME: this does not work
-	if (style && parent.div.layout != LAYOUT_FLOATING) {
-		bounds.x += ctx.style.margin.x;
-		bounds.y += ctx.style.margin.y;
-
-		// total keep-out borders
-		Rect margin_tot = {
-		    .x = ctx.style.padding.x + ctx.style.border.x +
-		         ctx.style.margin.x,
-		    .y = ctx.style.padding.y + ctx.style.border.y +
-		         ctx.style.margin.y,
-		    .w = ctx.style.padding.w + ctx.style.border.x +
-		         ctx.style.margin.w,
-		    .h = ctx.style.padding.h + ctx.style.border.x +
-		         ctx.style.margin.h,
-		};
-
-		parent.div.origin_r.x += margin_tot.x + margin_tot.w;
-		// parent.div.origin_r.y += margin_tot.h;
-
-		// parent.div.origin_c.x += margin_tot.w;
-		parent.div.origin_c.y += margin_tot.y + margin_tot.h;
+	// 4. Calculate the "scrolled" view
+	Point off;
+	if (parent.div.can_scroll_x && parent.div.horizontal_scroll_bar != -1) {
+		Elem*! sx = ctx.get_elem_by_tree_idx(parent.div.horizontal_scroll_bar);
+		if (catch sx) { return Rect{}; }
+		// TODO: assert that the element is a slider
+		off.x = (short)(parent.div.children_bounds.w * sx.slider.value);
+	}
+	if (parent.div.can_scroll_y && parent.div.vertical_scroll_bar != -1) {
+		Elem*! sy = ctx.get_elem_by_tree_idx(parent.div.vertical_scroll_bar);
+		if (catch sy) { return Rect{}; }
+		// TODO: assert that the element is a slider
+		off.y = (short)(parent.div.children_bounds.h * sy.slider.value);
 	}
+	Rect view = {
+		.x = parent.bounds.x + off.x,
+		.y = parent.bounds.y + off.y,
+		.w = parent.bounds.w,
+		.h = parent.bounds.h,
+	};
+
+	// TODO: 5. check if the placement is inside the view
 
-	return bounds;
+	return placement;
 }