Nicer plot

Change-Id: I6f080a4c26ad8ce574661228a4d4b53632d2f870

app/plot.cpp

@@ -0,0 +1,73 @@
+extern "C" {
+#include <assert.h>
+#include <kandinsky.h>
+#include <stdlib.h>
+#include <ion.h>
+}
+
+#include <poincare.h>
+
+#include "utils.h"
+#include "plot.h"
+
+constexpr KDCoordinate kScreenWidth = SCREEN_WIDTH;
+const KDCoordinate kScreenHeight = SCREEN_HEIGHT;
+
+// For now we only plot the axes at the origin.
+// TODO: print axes not at the origin with some values too.
+// TODO: label the axes.
+// TODO: put the values on the axes.
+static void plot_axes(float xMin, float xMax, float yMin, float yMax) {
+  if (xMin < 0 && xMax > 0) {
+    float total = xMax - xMin;
+    float ratio = xMax / total;
+    KDCoordinate width = ratio * kScreenWidth;
+    KDDrawLine(KDPointMake(width, 0), KDPointMake(width, kScreenHeight-1), 0xff);
+  }
+  if (yMin < 0 && yMax > 0) {
+    float total = yMax - yMin;
+    float ratio = yMax / total;
+    KDCoordinate height = ratio * kScreenHeight;
+    KDDrawLine(KDPointMake(0, height), KDPointMake(kScreenWidth-1, height), 0xff);
+  }
+}
+
+// TODO: Add a cursor.
+// TODO: print the expression.
+void plot(Expression * e, float xMin, float xMax, float yMin, float yMax) {
+  assert(e);
+
+  Context plotContext;
+
+  // Plot the original axes.
+  plot_axes(xMin, xMax, yMin, yMax);
+
+  // We need to initialize the first point.
+  Float xExp = Float(xMin);
+  plotContext.setExpressionForSymbolName(&xExp, "x");
+  float y = e->approximate(plotContext);
+  KDCoordinate j = ((y-yMin) / (yMax-yMin) * kScreenHeight);
+  if (j < 0) {
+    j = 0;
+  } else if (j >= kScreenHeight) {
+    j = kScreenHeight - 1;
+  }
+  KDPoint previousPoint = KDPointMake(0, kScreenHeight-j);
+
+  for (KDCoordinate i = 1; i < kScreenWidth; i++) {
+    float x = xMin + (xMax-xMin)/kScreenWidth*i;
+    Float xExp = Float(x);
+    plotContext.setExpressionForSymbolName(&xExp, "x");
+    float y = e->approximate(plotContext);
+    KDCoordinate j = ((y-yMin) / (yMax-yMin) * kScreenHeight);
+    KDPoint currentPoint = KDPointMake(i, kScreenHeight-j);
+    if (currentPoint.y < 0) {
+      currentPoint.y = 0;
+    } else if (currentPoint.y >= kScreenHeight) {
+      currentPoint.y = kScreenHeight - 1;
+    }
+    KDDrawLine(previousPoint, currentPoint, 0xFF);
+    previousPoint = currentPoint;
+  }
+  ion_get_event(); // We wait for a text input.
+}