Help: Populate tutorial guide text

Migrate tutorial text from individual `directions.txt` files to the main
tutorial document.  Add some comments to source code to provide anchors
for inclusion.

4 files changed, 5 insertions, 106 deletions

diff --git a/Help/guide/tutorial/Step6/CMakeLists.txt b/Help/guide/tutorial/Step6/CMakeLists.txt
index a78b0ff..5829891 100644
--- a/Help/guide/tutorial/Step6/CMakeLists.txt
+++ b/Help/guide/tutorial/Step6/CMakeLists.txt
@@ -3,7 +3,7 @@ project(Tutorial)
 
 set(CMAKE_CXX_STANDARD 14)
 
-# the version number.
+# set the version number
 set(Tutorial_VERSION_MAJOR 1)
 set(Tutorial_VERSION_MINOR 0)
 
diff --git a/Help/guide/tutorial/Step6/MathFunctions/CMakeLists.txt b/Help/guide/tutorial/Step6/MathFunctions/CMakeLists.txt
index 2946075..def1140 100644
--- a/Help/guide/tutorial/Step6/MathFunctions/CMakeLists.txt
+++ b/Help/guide/tutorial/Step6/MathFunctions/CMakeLists.txt
@@ -4,11 +4,11 @@ add_library(MathFunctions mysqrt.cxx)
 # to find MathFunctions.h, while we don't.
 # state that we depend on Tutorial_BINARY_DIR but consumers don't, as the
 # TutorialConfig.h include is an implementation detail
-
 target_include_directories(MathFunctions
           INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
           PRIVATE ${Tutorial_BINARY_DIR}
           )
 
+# install rules
 install(TARGETS MathFunctions DESTINATION lib)
 install(FILES MathFunctions.h DESTINATION include)
diff --git a/Help/guide/tutorial/Step6/directions.txt b/Help/guide/tutorial/Step6/directions.txt
deleted file mode 100644
index 42b9f06..0000000
--- a/Help/guide/tutorial/Step6/directions.txt
+++ /dev/null
@@ -1,104 +0,0 @@
-# Adding a Custom Command and Generated File #
-
-In this section we will show how you can add a generated source file into the
-build process of an application. For this example, we will create a table of
-precomputed square roots as part of the build process, and then compile that
-table into our application.
-
-To accomplish this, we first need a program that will generate the table. In the
-MathFunctions subdirectory a new source file named MakeTable.cxx will do just that.
-
-  // A simple program that builds a sqrt table
-  #include <iostream>
-  #include <fstream>
-  #include <cmath>
-
-  int main (int argc, char *argv[])
-  {
-    // make sure we have enough arguments
-    if (argc < 2) {
-      return 1;
-    }
-
-    std::ofstream fout(argv[1],std::ios_base::out);
-    const bool fileOpen = fout.is_open();
-    if(fileOpen) {
-      fout << "double sqrtTable[] = {" << std::endl;
-      for (int i = 0; i < 10; ++i) {
-        fout << sqrt(static_cast<double>(i)) << "," << std::endl;
-      }
-      // close the table with a zero
-      fout << "0};" << std::endl;
-      fout.close();
-    }
-    return fileOpen ? 0 : 1; // return 0 if wrote the file
-  }
-
-Note that the table is produced as valid C++ code and that the output filename
-is passed in as an argument.
-
-The next step is to add the appropriate commands to MathFunctions’ CMakeLists
-file to build the MakeTable executable and then run it as part of the build
-process. A few commands are needed to accomplish this, as shown below:
-
-  # first we add the executable that generates the table
-  add_executable(MakeTable MakeTable.cxx)
-
-  # add the command to generate the source code
-  add_custom_command(
-    OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.h
-    COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h
-    DEPENDS MakeTable
-    )
-
-  # add the main library
-  add_library(MathFunctions
-              mysqrt.cxx
-              ${CMAKE_CURRENT_BINARY_DIR}/Table.h
-              )
-
-  target_include_directories(MathFunctions
-          INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
-          PUBLIC ${Tutorial_BINARY_DIR}
-                 # add the binary tree directory to the search path for include files
-                 ${CMAKE_CURRENT_BINARY_DIR}
-          )
-
-  install(TARGETS MathFunctions DESTINATION lib)
-  install(FILES MathFunctions.h DESTINATION include)
-
-First, the executable for MakeTable is added as any other executable would be
-added. Then we add a custom command that specifies how to produce Table.h by
-running MakeTable. Next we have to let CMake know that mysqrt.cxx depends on
-the generated file Table.h. This is done by adding the generated Table.h to the
-list of sources for the library MathFunctions. We also have to add the current
-binary directory to the list of include directories so that Table.h can be
-found and included by mysqrt.cxx.
-
-Now let's use the generated table. First, modify mysqrt.cxx to include Table.h.
-Next, we can rewrite the mysqrt function to use the table:
-
-  if (x <= 0) {
-    return 0;
-  }
-
-  // use the table to help find an initial value
-  double result = x;
-  if (x >= 1 && x < 10) {
-    result = sqrtTable[static_cast<int>(x)];
-  }
-
-  // do ten iterations
-  for (int i = 0; i < 10; ++i) {
-    if (result <= 0) {
-      result = 0.1;
-    }
-    double delta = x - (result*result);
-    result = result + 0.5*delta/result;
-    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
-  }
-
-Run cmake or cmake-gui to configure the project and then build it with your
-chosen build tool. When this project is built it will first build the MakeTable
-executable. It will then run MakeTable to produce Table.h. Finally, it will
-compile mysqrt.cxx which includes Table.h to produce the MathFunctions library.
diff --git a/Help/guide/tutorial/Step6/tutorial.cxx b/Help/guide/tutorial/Step6/tutorial.cxx
index c2b89df..8156a9c 100644
--- a/Help/guide/tutorial/Step6/tutorial.cxx
+++ b/Help/guide/tutorial/Step6/tutorial.cxx
@@ -5,6 +5,7 @@
 
 #include "TutorialConfig.h"
 
+// should we include the MathFunctions header?
 #ifdef USE_MYMATH
 #  include "MathFunctions.h"
 #endif
@@ -12,6 +13,7 @@
 int main(int argc, char* argv[])
 {
   if (argc < 2) {
+    // report version
     std::cout << argv[0] << " Version " << Tutorial_VERSION_MAJOR << "."
               << Tutorial_VERSION_MINOR << std::endl;
     std::cout << "Usage: " << argv[0] << " number" << std::endl;
@@ -20,6 +22,7 @@ int main(int argc, char* argv[])
 
   double inputValue = std::stod(argv[1]);
 
+  // which square root function should we use?
 #ifdef USE_MYMATH
   double outputValue = mysqrt(inputValue);
 #else