/// <summary>
/// Plots this equation explicitly on the graph. This is faster than implicit plotting but plotting explicitly with respect
/// to a variable (eg. <c>'y'</c>) requires that variable to occur once and once only in an equation, alone on one side of
/// the equation. For example, the equation <c>y=x^2-3x+2</c> explicitly defines the value of y, but <c>y^2+x^2=4</c> does not,
/// instead using it generally in the terms of the equation. This method plots <paramref name="explicitVariable"/> on the
/// vertical axis of <paramref name="graph"/>.
/// </summary>
/// <param name="graph">The Graph to plot this IPlottable onto.</param>
/// <param name="graphics">The GDI+ drawing surface to use for plotting this IPlottable.</param>
/// <param name="graphSize">The size of the Graph on the screen. This is a property of the display rather than the
/// graph and is thus not included in the graph's parameters.</param>
/// <param name="graphPen">The pen to use for drawing the curve of the equation.</param>
/// <param name="resolution">The plotting resolution to use. Using a coarser resolution may make the plotting
/// process faster, and is thus more suitable when the display is being resized or moved.</param>
/// <param name="explicitVariable">The variable that is explicitly defined.</param>
/// <param name="node">The parse tree node representing what <paramref name="explicitVariable"/> is explicitly equal to.</param>
private void PlotExplicitVertical(Graph graph, Graphics graphics, Size graphSize, Pen graphPen, char explicitVariable, ParseTreeNode node, PlotResolution resolution)
{
VariableSet vars = new VariableSet();
int previousX = -1, previousY = -1;
// use wider intervals for coarser plot resolutions
float interval = 0.1f;
if (resolution == PlotResolution.Resize)
{
interval *= 100f;
}
if (resolution == PlotResolution.Edit)
{
interval *= 40f;
}
// evaluate the equation at every point along the axis and plot accordingly
for (float i = 0; i < graphSize.Width; i += interval)
{
double vertical = graph.Parameters.VerticalPixelScale * -(i - graphSize.Height / 2) + graph.Parameters.CenterVertical;
vars[explicitVariable] = vertical;
double horizontal = node.Evaluate(vars);
int x, y;
graph.ToImageSpace(graphSize, horizontal, vertical, out x, out y);
if (previousX != -1)
{
if (x < -100 || x >= graphSize.Width + 100)
{
x = -1;
y = -1;
}
else
{
try
{
graphics.DrawLine(graphPen, previousX, previousY, x, y);
}
catch (OverflowException) // can happen if the graph line shoots up tending to infinity
{
x = -1;
y = -1;
}
}
}
previousX = x;
previousY = y;
}
}
