OpenGL Pentagon Example

Fall 2013

• v1.cpp, which draws a polygon using immediate-mode calls to glVertex
• v2.cpp, which replaces the now-deprecated GL_POLYGON with three GL_TRIANGLES
• v3.cpp, which moves the vertices into a client-side array, which we index into in calling glVertex
• v4.cpp, which replaces nine calls to glVertex with one call to glDrawArrays. In order to do this, it needs to use OpenGL's "client-side vertex array" -- a client-side array that OpenGL knows about, so it can retrieve the data from it
• v5.cpp, which replaces glDrawArrays with glDrawElements. This allows us to specify only the indices of the vertices rather than re-specifying the vertices themselves
• v6.cpp, which stores the array of vertices in a "buffer" on the GPU rather than on the client side. This is the first version that needs to explicitly identify what attribute(s) it's sharing with the GLSL program. (I'm not sure how previous versions got away without that....)
• v7.cpp, which uses TWO buffers -- one for vertex positions and one for vertex colors -- "wrapped up" in a single vertex array object. The result is a smear of color that my wife calls a "rainbow pentagon". (To handle color, we need different vertex and fragment shaders; see vpassthru.glsl and fpassthru.glsl.)
• v8.cpp, which replaces the smear of color with several monochromatic triangles. (This program uses the same shaders as version 7.)
• More versions to come, as I figure out how to make them work...
• AngelInitShader.cpp, which all of the above main programs use to read in the GLSL programs
• GrecoInitShader.cpp, Dan Greco's modified version of the above. (I then modified it further. The version I've posted here is working for me, from the command line, and I think it works in Visual Studio as well.)
• Angel.h, my slightly modified version of Angel's header file, declaring InitShader to take in string parameters rather than const char *. You'll also need to make sure you have Angel's supporting header files mat.h, vec.h, and perhaps CheckError.h. Oddly enough, Angel supplies about five not-quite-identical versions of each of those files; it's not clear which one is best to use.
• Makefile, which controls the compiling-and-linking process. You should be able to type make v4, and it'll compile and link v4.cpp to produce an executable named v4, which you can then run directly.
• vshader21.glsl, the vertex shader program for versions 1-6
• fshader21.glsl, the fragment shader program for versions 1-6
• init-shader.rkt, a Racket version of InitShader.cpp, to go with the following...
• v1.rkt, a Racket version of v1.cpp
• v2.rkt, a Racket version of v2.cpp
• v3.rkt, a Racket version of v3.cpp
• v4.rkt, a Racket version of v4.cpp
• v5.rkt, a Racket version of v5.cpp
• v6.rkt, a Racket version of v6.cpp