From 61854d118e350cd0d6bfaf8a02880d54409e45da Mon Sep 17 00:00:00 2001
From: Romain Goyet <romain.goyet@numworks.com>
Date: Thu, 21 Apr 2016 17:14:59 +0200
Subject: [PATCH] Kandinsky: Add KDRectIntersect and update KDRectIntersection

One gives a boolean, the other the actual KDRect

Change-Id: I5a2e6d1110f0ad111ac2f3a46dcd072e72ea786d
---
 escher/src/view.cpp                |  4 +--
 kandinsky/include/kandinsky/rect.h |  5 ++-
 kandinsky/src/rect.c               | 58 +++++++++++++++---------------
 3 files changed, 36 insertions(+), 31 deletions(-)

diff --git a/escher/src/view.cpp b/escher/src/view.cpp
index 11e0e4b5a..a4ac70062 100644
--- a/escher/src/view.cpp
+++ b/escher/src/view.cpp
@@ -34,8 +34,8 @@ void View::redraw(KDRect rect) {
     if (subview == nullptr) {
       continue;
     }
-    KDRect intersection = KDRectIntersect(rect, subview->m_frame);
-    if (intersection.width > 0 || intersection.height > 0) {
+    if (KDRectIntersect(rect, subview->m_frame)) {
+      KDRect intersection = KDRectIntersection(rect, subview->m_frame);
       // Let's express intersection in subview's coordinates
       intersection.x -= subview->m_frame.x;
       intersection.y -= subview->m_frame.y;
diff --git a/kandinsky/include/kandinsky/rect.h b/kandinsky/include/kandinsky/rect.h
index e05389256..fe820db85 100644
--- a/kandinsky/include/kandinsky/rect.h
+++ b/kandinsky/include/kandinsky/rect.h
@@ -1,6 +1,7 @@
 #ifndef KANDINSKY_RECT_H
 #define KANDINSKY_RECT_H
 
+#include <stdbool.h>
 #include <kandinsky/color.h>
 #include <kandinsky/types.h>
 
@@ -22,7 +23,9 @@ typedef struct {
 } KDRect;
 
 extern KDRect KDRectZero;
-KDRect KDRectIntersect(KDRect r1, KDRect r2);
+
+bool KDRectIntersect(KDRect r1, KDRect r2);
+KDRect KDRectIntersection(KDRect r1, KDRect r2);
 
 void KDFillRect(KDRect rect, KDColor color);
 void KDDrawRect(KDRect rect, KDColor color);
diff --git a/kandinsky/src/rect.c b/kandinsky/src/rect.c
index cb59e0311..1dc626994 100644
--- a/kandinsky/src/rect.c
+++ b/kandinsky/src/rect.c
@@ -4,38 +4,40 @@
 
 KDRect KDRectZero = {.x = 0, .y = 0, .width = 0, .height = 0};
 
-KDRect KDRectIntersect(KDRect r1, KDRect r2) {
-  KDRect intersection;
+static inline KDCoordinate left(KDRect r) { return r.x; }
+static inline KDCoordinate right(KDRect r) { return r.x+r.width; }
+static inline KDCoordinate top(KDRect r) { return r.y; }
+static inline KDCoordinate bottom(KDRect r) { return r.y+r.height; }
+static inline KDCoordinate min(KDCoordinate x, KDCoordinate y) { return (x<y ? x : y); }
+static inline KDCoordinate max(KDCoordinate x, KDCoordinate y) { return (x>y ? x : y); }
 
-  // Let's start by computing the overlap on the X axis
-  if (r1.x < r2.x) {
-    intersection.x = r2.x;
-    intersection.width = r1.x+r1.width-r2.x;
-  } else {
-    intersection.x = r1.x;
-    intersection.width = r2.x+r2.width-r1.x;
-  }
+bool KDRectIntersect(KDRect r1, KDRect r2) {
+    return !(right(r2) < left(r1)
+             ||
+             left(r2) > right(r1)
+             ||
+             top(r2) > bottom(r1)
+             ||
+             bottom(r2) < top(r1)
+             );
+}
 
-  if (intersection.width < 0) {
-    // There's no overlap on the X axis, let's bail out
-    return KDRectZero;
-  }
+KDRect KDRectIntersection(KDRect r1, KDRect r2) {
+    if (!KDRectIntersect(r1, r2)) {
+        return KDRectZero;
+    }
 
-  // Let's then compute the overlap on the Y axis
-  if (r1.y < r2.y) {
-    intersection.y = r2.y;
-    intersection.height = r1.y+r1.height-r2.y;
-  } else {
-    intersection.y = r1.y;
-    intersection.height = r2.y+r2.height-r1.y;
-  }
+    KDCoordinate intersectionLeft = max(left(r1), left(r2));
+    KDCoordinate intersectionRight = min(right(r1), right(r2));
+    KDCoordinate intersectionTop = max(top(r1), top(r2));
+    KDCoordinate intersectionBottom = min(bottom(r1), bottom(r2));
 
-  if (intersection.height < 0) {
-    // There's no overlap on the Y axis, let's bail out
-    return KDRectZero;
-  }
-
-  return intersection;
+    KDRect intersection;
+    intersection.x = intersectionLeft;
+    intersection.width = intersectionRight-intersectionLeft;
+    intersection.y = intersectionTop;
+    intersection.height = intersectionBottom-intersectionTop;
+    return intersection;
 }
 
 void KDFillRect(KDRect rect, KDColor color) {