docs: Added tests for Simple Image input and updated rst (#4019)

Added the simple input tests from the ImageInput chapter of the docs as
C++ and Python examples, a part of the larger issue #3992 . Followed
prototype
(https://github.com/AcademySoftwareFoundation/OpenImageIO/wiki/Converting-documentation-examples-to-tests)
approach.

---------

Signed-off-by: CalvinSch <[email protected]>

Author: CalvinSch

src/doc/imageinput.rst

@@ -20,35 +20,16 @@ memory, even if that's not the way they're stored in the file):
 
 .. tabs::
 
-    .. code-tab:: c++
-
-        #include <OpenImageIO/imageio.h>
-        using namespace OIIO;
-        ...
-
-        auto inp = ImageInput::open(filename);
-        if (! inp)
-            return;
-        const ImageSpec &spec = inp->spec();
-        int xres = spec.width;
-        int yres = spec.height;
-        int nchannels = spec.nchannels;
-        auto pixels = std::unique_ptr<unsigned char[]>(new unsigned char[xres * yres * nchannels]);
-        inp->read_image(0, 0, 0, nchannels, TypeDesc::UINT8, &pixels[0]);
-        inp->close();
-
+    .. tab:: C++
+        .. literalinclude:: ../../testsuite/docs-examples-cpp/src/docs-examples-imageinput.cpp
+            :language: c++
+            :start-after: BEGIN-imageinput-simple
+            :end-before: END-imageinput-simple
     .. code-tab:: py
-
-        import OpenImageIO as oiio
-
-        inp = oiio.ImageInput.open(filename)
-        if inp :
-            spec = inp.spec()
-            xres = spec.width
-            yres = spec.height
-            nchannels = spec.nchannels
-            pixels = inp.read_image(0, 0, 0, nchannels, "uint8")
-            inp.close()
+        .. literalinclude:: ../../testsuite/docs-examples-python/src/docs-examples-imageinput.py
+            :language: py
+            :start-after: BEGIN-imageinput-simple
+            :end-before: END-imageinput-simple
 
 Here is a breakdown of what work this code is doing:
 

testsuite/docs-examples-cpp/src/docs-examples-imageinput.cpp

@@ -32,10 +32,34 @@ void example1()
 
 
 
+// BEGIN-imageinput-simple
+#include <OpenImageIO/imageio.h>
+using namespace OIIO;
+
+void simple_read()
+{
+    const char* filename = "tahoe.tif";
+
+    auto inp = ImageInput::open(filename);
+    if (! inp)
+        return;
+    const ImageSpec &spec = inp->spec();
+    int xres = spec.width;
+    int yres = spec.height;
+    int nchannels = spec.nchannels;
+    auto pixels = std::unique_ptr<unsigned char[]>(new unsigned char[xres * yres * nchannels]);
+    inp->read_image(0, 0, 0, nchannels, TypeDesc::UINT8, &pixels[0]);
+    inp->close();
+}
+
+// END-imageinput-simple
+
+
+
 int main(int /*argc*/, char** /*argv*/)
 {
     // Each example function needs to get called here, or it won't execute
     // as part of the test.
-    example1();
+    simple_read();
     return 0;
 }

testsuite/docs-examples-python/src/docs-examples-imageinput.py

@@ -37,10 +37,24 @@ def example1() :
 ############################################################################
 
 
+# BEGIN-impageinput-simple
+import OpenImageIO as oiio
+def simple_read():
+    filename = "tahoe.tif"
+
+    inp = oiio.ImageInput.open(filename)
+    if inp :
+        spec = inp.spec()
+        xres = spec.width
+        yres = spec.height
+        nchannels = spec.nchannels
+        pixels = inp.read_image(0, 0, 0, nchannels, "uint8")
+        inp.close()
+# END-imageinput-simple
 
 
 
 if __name__ == '__main__':
     # Each example function needs to get called here, or it won't execute
     # as part of the test.
-    example1()
+    simple_read()