Reworked the "new" bridging to respect the bridge_flow_ratio

by maintaining extrusion spacing, but modifying the extrusion width
and / or height.

src/libslic3r/Flow.cpp

@@ -6,12 +6,6 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 
-// Overlap factor of perimeter lines. Currently no overlap.
-// #define HAS_PERIMETER_LINE_OVERLAP
-#ifdef HAS_PERIMETER_LINE_OVERLAP
-    #define PERIMETER_LINE_OVERLAP_FACTOR 1.0
-#endif
-
 // Mark string for localization and translate.
 #define L(s) Slic3r::I18N::translate(s)
 
@@ -142,62 +136,82 @@ Flow Flow::new_from_config_width(FlowRole role, const ConfigOptionFloatOrPercent
         w = float(width.get_abs_value(height));
     }
     
-    return Flow(w, height, nozzle_diameter, false);
+    return Flow(w, height, rounded_rectangle_extrusion_spacing(w, height), nozzle_diameter, false);
 }
 
-// This constructor builds a Flow object from a given centerline spacing.
-Flow Flow::new_from_spacing(float spacing, float nozzle_diameter, float height) 
+// Adjust extrusion flow for new extrusion line spacing, maintaining the old spacing between extrusions.
+Flow Flow::with_spacing(float new_spacing) const
 {
-    if (height <= 0) 
-        throw Slic3r::InvalidArgument("Invalid flow height supplied to new_from_spacing()");
-    // Calculate width from spacing.
-    // For normal extrusons, extrusion width is wider than the spacing due to the rounding and squishing of the extrusions.
-    float width = float(
-#ifdef HAS_PERIMETER_LINE_OVERLAP
-        (spacing + PERIMETER_LINE_OVERLAP_FACTOR * height * (1. - 0.25 * PI));
-#else
-        (spacing + height * (1. - 0.25 * PI)));
-#endif
-    return Flow(width, height, nozzle_diameter);
+    Flow out = *this;
+    if (m_bridge) {
+        // Diameter of the rounded extrusion.
+        assert(m_width == m_height);
+        float gap          = m_spacing - m_width;
+        auto  new_diameter = new_spacing - gap;
+        out.m_width        = out.m_height = new_diameter;
+    } else {
+        out.m_width += new_spacing - m_spacing;
+        if (out.m_width < out.m_height)
+            throw Slic3r::InvalidArgument("Invalid spacing supplied to Flow::with_spacing()");
+    }
+    out.m_spacing = new_spacing;
+    return out;
 }
 
-// This method returns the centerline spacing between two adjacent extrusions 
-// having the same extrusion width (and other properties).
-float Flow::spacing() const 
+// Adjust the width / height of a rounded extrusion model to reach the prescribed cross section area while maintaining extrusion spacing.
+Flow Flow::with_cross_section(float area_new) const
 {
-#ifdef HAS_PERIMETER_LINE_OVERLAP
-    if (m_bridge)
-        return m_width + BRIDGE_EXTRA_SPACING;
-    // rectangle with semicircles at the ends
-    float min_flow_spacing = m_width - m_height * (1. - 0.25 * PI);
-    float res = m_width - PERIMETER_LINE_OVERLAP_FACTOR * (m_width - min_flow_spacing);
-#else
-    float res = float(m_bridge ? (m_width + BRIDGE_EXTRA_SPACING) : (m_width - m_height * (1. - 0.25 * PI)));
-#endif
-//    assert(res > 0.f);
-	if (res <= 0.f)
-		throw FlowErrorNegativeSpacing();
-	return res;
+    assert(! m_bridge);
+    assert(flow.width() >= flow.height());
+
+    // Adjust for bridge_flow_ratio, maintain the extrusion spacing.
+    float area = this->mm3_per_mm();
+    if (area_new > area + EPSILON) {
+        // Increasing the flow rate.
+        float new_full_spacing = area_new / m_height;
+        if (new_full_spacing > m_spacing) {
+            // Filling up the spacing without an air gap. Grow the extrusion in height.
+            float height = area_new / m_spacing;
+            return Flow(rounded_rectangle_extrusion_width_from_spacing(m_spacing, height), height, m_spacing, m_nozzle_diameter, false);
+        } else {
+            return this->with_width(rounded_rectangle_extrusion_width_from_spacing(area / m_height, m_height));
+        }
+    } else if (area_new < area - EPSILON) {
+        // Decreasing the flow rate.
+        float width_new = m_width - (area - area_new) / m_height;
+        assert(width_dif > 0);
+        if (width_new > m_height) {
+            // Shrink the extrusion width.
+            return this->with_width(width_new);
+        } else {
+            // Create a rounded extrusion.
+            auto dmr = float(sqrt(area_new / M_PI));
+            return Flow(dmr, dmr, m_spacing, m_nozzle_diameter, false);
+        }
+    } else
+        return *this;
 }
 
-// This method returns the centerline spacing between an extrusion using this
-// flow and another one using another flow.
-// this->spacing(other) shall return the same value as other.spacing(*this)
-float Flow::spacing(const Flow &other) const
+float Flow::rounded_rectangle_extrusion_spacing(float width, float height)
 {
-    assert(m_height == other.m_height);
-    assert(m_bridge == other.m_bridge);
-    float res = float(m_bridge ? 
-        0.5 * m_width + 0.5 * other.m_width + BRIDGE_EXTRA_SPACING :
-        0.5 * this->spacing() + 0.5 * other.spacing());
-//    assert(res > 0.f);
-	if (res <= 0.f)
-		throw FlowErrorNegativeSpacing();
-	return res;
+    auto out = width - height * float(1. - 0.25 * PI);
+    if (out <= 0.f)
+        throw FlowErrorNegativeSpacing();
+    return out;
+}
+
+float Flow::rounded_rectangle_extrusion_width_from_spacing(float spacing, float height)
+{
+    return float(spacing + height * (1. - 0.25 * PI));
+}
+
+float Flow::bridge_extrusion_spacing(float dmr)
+{
+    return dmr + BRIDGE_EXTRA_SPACING;
 }
 
 // This method returns extrusion volume per head move unit.
-double Flow::mm3_per_mm() const 
+double Flow::mm3_per_mm() const
 {
     float res = m_bridge ?
         // Area of a circle with dmr of this->width.