Vinicius Cole

Side-Scrolling Game in C++ and OpenGL

A side-scrolling shooter in C++ with OpenGL and GLUT, reading its arena from an SVG file, compiled to WebAssembly to run here.

  • C++
  • OpenGL
  • GLUT
  • Emscripten
  • WebAssembly
github.com/viniciuscole/2D-Computer-Graphics

Loads about 380 KB: the WebAssembly game, its loader and the arena.

Controls

  • A D — walk
  • Right mouse button or W — hold to jump; the longer you hold, the higher
  • Left mouse button — shoot
  • Move the mouse — aim the arm
  • R — restart

SVG arena parsed with tinyxml2 (zlib licence).

The game reads its arena from an SVG file: the blue rectangle is the field, black rectangles are obstacles, the green circle marks where the player starts and the red ones mark the opponents (seven of them). The circles only carry position and scale — each character is drawn from scratch around them, with a head, a torso, an articulated arm and two legs hinged at hip and knee, animated as they walk. The arm follows the mouse, and the left button fires.

The arena is nine screens wide; the square window tracks the player horizontally. The goal is to cross from left to right without being hit.

All rendering uses immediate-mode OpenGL — glBegin, glVertex2f, glOrtho — and the SVG is parsed with tinyxml2 (zlib licence), compiled in.

What it cost to bring here

Emscripten compiles the C++ to WebAssembly, but it does not implement everything GLUT offers. Two things had to change.

GL_POLYGON, used to draw the circles, does not exist in its immediate-mode emulation: the program compiled and linked without complaint, then aborted on the first frame. Swapped for GL_TRIANGLE_FAN, which draws exactly the same thing for a convex polygon.

The end-of-game messages were drawn with GLUT bitmap fonts, which Emscripten also lacks. They became HTML over the canvas — which, as a side effect, got them translated.

The two changes reached the code differently. The GL_POLYGON swap is a plain substitution, with no guard at all — harmless for the native build because, as already noted, the triangle fan draws the same thing as the polygon for a convex shape. The message swap, though, sits inside an #ifdef __EMSCRIPTEN__ ... #else ... #endif block, keeping the original GLUT drawing in the #else branch.

The assignment’s own make still produces the native trabalhocg executable, with the messages drawn as they always were. The port didn’t replace the original — it gained a second target, by two different routes.

Beyond that, the game here is the one that runs natively: the roughly 180 KB of WebAssembly on this page are the project’s own C++, compiled. There is no emulator in between.