From eed0f4af9598ca7787240eab807dd1c5a05ba358 Mon Sep 17 00:00:00 2001
From: Romain Goyet <romain.goyet@numworks.com>
Date: Tue, 21 Jun 2016 11:45:58 +0200
Subject: [PATCH] Graph: Draw axis and grid

Change-Id: I06d01dfbf7f45920aa32fd5c85819c75309fbfc4
---
 apps/graph/graph/graph_view.cpp | 99 +++++++++++++++++++++++++--------
 apps/graph/graph/graph_view.h   | 17 ++++++
 2 files changed, 93 insertions(+), 23 deletions(-)

diff --git a/apps/graph/graph/graph_view.cpp b/apps/graph/graph/graph_view.cpp
index 818013218..fbf6e132e 100644
--- a/apps/graph/graph/graph_view.cpp
+++ b/apps/graph/graph/graph_view.cpp
@@ -1,9 +1,19 @@
 #include "graph_view.h"
 
+constexpr KDColor kAxisColor = KDColorGray(0x0);
+constexpr KDColor kMainGridColor = KDColorGray(0xCC);
+constexpr KDColor kSecondaryGridColor = KDColorGray(0xEE);
+constexpr int kNumberOfMainGridLines = 5;
+constexpr int kNumberOfSecondaryGridLines = 5;
+
 GraphView::GraphView() :
   View(),
   m_cursorView(CursorView()),
-  m_cursorPosition(KDPointZero)
+  m_cursorPosition(KDPointZero),
+  m_xMin(-2.0f),
+  m_xMax(2.0f),
+  m_yMin(-2.0f),
+  m_yMax(2.0f)
 {
 }
 
@@ -30,29 +40,72 @@ void GraphView::layoutSubviews() {
 
 void GraphView::drawRect(KDRect rect) const {
   KDFillRect(rect, KDColorWhite);
-  KDCoordinate x_grid_step = m_frame.width/10;
-  KDCoordinate y_grid_step = m_frame.height/10;
-  KDColor gridColor = KDColorGray(0xEE);
-  for (KDCoordinate x=0; x<m_frame.width; x += x_grid_step) {
-    KDRect verticalGridRect;
-    verticalGridRect.x = x;
-    verticalGridRect.y = 0;
-    verticalGridRect.width = 1;
-    verticalGridRect.height = m_frame.height;
-    KDFillRect(verticalGridRect, gridColor);
+  drawGrid(rect);
+  drawAxis(rect);
+  drawFunction(rect);
+}
+
+void GraphView::drawHorizontalLine(KDRect rect, float y, KDColor color) const {
+  KDRect lineRect;
+  lineRect.x = rect.x;
+  lineRect.y = floatToYPixel(y);
+  lineRect.width = rect.width;
+  lineRect.height = 1;
+  KDFillRect(lineRect, color);
+}
+
+void GraphView::drawVerticalLine(KDRect rect, float x, KDColor color) const {
+  KDRect lineRect;
+  lineRect.x = floatToXPixel(x);
+  lineRect.y = rect.y;
+  lineRect.width = 1;
+  lineRect.height = rect.height;
+  KDFillRect(lineRect, color);
+}
+
+void GraphView::drawAxis(KDRect rect) const {
+  drawHorizontalLine(rect, 0.0f, kAxisColor);
+  drawVerticalLine(rect, 0.0f, kAxisColor);
+}
+
+void GraphView::drawGrid(KDRect rect) const {
+  float xRange = m_xMax - m_xMin;
+  float xGridStep = xRange/kNumberOfMainGridLines;
+  float xGridStart = xGridStep*((int)(m_xMin/xGridStep));
+  for (int i=0; i<kNumberOfMainGridLines; i++) {
+    drawVerticalLine(rect, xGridStart+i*xGridStep, kMainGridColor);
   }
-  for (KDCoordinate y=0; y<m_frame.height; y += y_grid_step) {
-    KDRect horizontalGridRect;
-    horizontalGridRect.x = 0;
-    horizontalGridRect.y = y;
-    horizontalGridRect.width = m_frame.width;
-    horizontalGridRect.height = 1;
-    KDFillRect(horizontalGridRect, gridColor);
+
+  float yRange = m_yMax - m_yMin;
+  float yGridStep = yRange/kNumberOfMainGridLines;
+  float yGridStart = yGridStep*((int)(m_yMin/yGridStep));
+  for (int i=0; i<kNumberOfMainGridLines; i++) {
+    drawHorizontalLine(rect, yGridStart+i*yGridStep, kMainGridColor);
   }
-  for (int i=0; i<m_frame.width; i++) {
-    KDPoint p;
-    p.x = i;
-    p.y = (i*i)/m_frame.height;
+}
+
+float GraphView::xPixelToFloat(int xPixel) const {
+  return m_xMin + xPixel*(m_xMax-m_xMin)/m_frame.width;
+}
+
+float GraphView::yPixelToFloat(int yPixel) const {
+  return m_yMin + yPixel*(m_yMax-m_yMin)/m_frame.height;
+}
+
+KDCoordinate GraphView::floatToYPixel(float y) const {
+  return m_frame.height*(m_yMax-y)/(m_yMax-m_yMin);
+}
+
+KDCoordinate GraphView::floatToXPixel(float x) const {
+  return m_frame.width*(m_xMax-x)/(m_xMax-m_xMin);
+}
+
+void GraphView::drawFunction(KDRect rect) const {
+  KDPoint p = KDPointZero;
+  for (p.x=rect.x; p.x<(rect.x+rect.width); p.x++) {
+    float x = xPixelToFloat(p.x);
+    float y = (x-1)*(x+1)*x;
+    p.y = floatToYPixel(y);
     KDSetPixel(p, KDColorRGB(0x7F, 0, 0));
   }
-};
+}
diff --git a/apps/graph/graph/graph_view.h b/apps/graph/graph/graph_view.h
index f192d5340..5fe3f0b73 100644
--- a/apps/graph/graph/graph_view.h
+++ b/apps/graph/graph/graph_view.h
@@ -14,8 +14,25 @@ private:
   View * subviewAtIndex(int index) override;
   void layoutSubviews() override;
 
+  float xPixelToFloat(int xPixel) const;
+  float yPixelToFloat(int yPixel) const;
+  KDCoordinate floatToXPixel(float x) const;
+  KDCoordinate floatToYPixel(float y) const;
+
+  void drawHorizontalLine(KDRect rect, float y, KDColor color) const;
+  void drawVerticalLine(KDRect rect, float x, KDColor color) const;
+
+  void drawAxis(KDRect rect) const;
+  void drawGrid(KDRect rect) const;
+  void drawFunction(KDRect rect) const;
+
   CursorView m_cursorView;
   KDPoint m_cursorPosition;
+
+  float m_xMin;
+  float m_xMax;
+  float m_yMin;
+  float m_yMax;
 };
 
 #endif