Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
Next are the declarations for our buffer arrays. We have three buffers named ExtMapBuffer(1-3).
We will change these array identifiers to something more descriptive shortly.
The init() function is where we set the properties for our indicator buffers. SetIndexBuffer()
binds a buffer array to a buffer index. The buffer index is what we refer to when we set the
properties for an indicator line, and also when we call an indicator line from an EA using the
iCustom() function. The first parameter is an integer from 0 to 7, and the second parameter is the
name of the buffer array.
Drawing Properties
The SetIndexStyle() function sets the type of line to draw, along with the properties of that line.
Every indicator line will have a corresponding SetIndexStyle() function. Here is the syntax:
void SetIndexStyle(int BufferIndex, int LineType, int LineStyle = EMPTY,
int LineWidth = EMPTY, color LineColor = CLR_NONE)
• BufferIndex – The index of the buffer, from 0 to 7.
• LineType – Sets the type of line to draw. DRAW_LINE draws a single line, DRAW_HISTOGRAM
draws a vertical histogram (see the OsMA or Awesome Oscillator indicators for examples),
DRAW_ARROW draws a symbol, and DRAW_NONE draws no line.
• LineStyle – An optional parameter indicating the drawing style. Used mainly for lines of type
DRAW_LINE. By default, a solid line is drawn (STYLE_SOLID). You can also draw dashed
(STYLE_DASH) and dotted (STYLE_DOT) lines.
• LineWidth – An optional parameter indicating the width of the line in pixels. The default
value is 1.
• LineColor – An optional parameter indicating the color of the line. If you use the wizard, the
color is set using #property declarations, but you can set the color here as well.
If you are using DRAW_ARROW as the LineType, the SetArrow() function allows you to set the
Wingdings font symbol to draw on the chart. The first parameter is the buffer index, and the second
is an integer constant representing the symbol to draw. The symbols can be found in the MQL
Reference under Standard Constants – Arrow Codes.
You may want to add a description for the indicator lines that will be displayed in the tooltip or in the
data window. To do this, use the SetIndexLabel() function. The first parameter is the buffer index,
and the second parameter is a text description. We'll add these to our indicator shortly.
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