JustDown

About This Project

JustDown is a 3D first-person environment implemented directly against the OpenGL 3.3 Core Profile API in C++17, without a pre-built game engine. It demonstrates real-time physics simulation, multi-light Phong shading, parallax-mapped surfaces, and a two-pass HDR bloom pipeline — all built from low-level primitives.

Players walk through the level, jump, observe from a free-fly debug camera, and take proportional fall damage when dropping from height. The level is defined by a plain-text .scene file; no recompilation needed to edit geometry, textures, or lighting.

Features

• Steep parallax mapping — per-pixel sub-layer linear interpolation reduces UV banding; layer count is view-angle-adaptive (mix(8, 32, dot(normal, viewDir)))
• HDR bloom pipeline — dual-attachment FBO for bright-pass extraction → 10-iteration separable Gaussian blur via ping-pong framebuffers → additive combine pass
• Physics movement — gravity, AABB collision response (floor vs. wall contact distinguished by center-to-center Y component), proportional fall damage
• Declarative .scene format — lists models, textures, positions, rotations, scales, and skybox; auto-selects shader variant by texture count
• Shader uniform cache — unordered_map in Shader avoids redundant glGetUniformLocation calls per frame

Technical Architecture

Application.cpp owns the main loop, initializes GLFW + GLAD, and threads delta time through the entire update stack for frame-rate-independent physics. Scene manages a flat list of Model instances, owns the shader pool and skybox, and dispatches each model to the correct shader variant. Player resolves horizontal movement relative to camera orientation, integrates gravity per frame, and delegates collision queries to Scene::checkPlayerCollision. PostProcess wraps the HDR framebuffer pipeline.

Model is header-only and handles OBJ parsing, GPU buffer setup (8-float layout for standard materials, 14-float for parallax), transformation, AABB computation, and rendering. All shaders load from files at runtime.

Engineering Highlights

Parallax mapping in tangent space — Requires per-vertex TBN matrix computed from per-face UV deltas using the inverse UV-parallelogram formula: f = 1 / det(UV_matrix), then tangent = f * (deltaUV2.y * edge1 - deltaUV1.y * edge2). The vertex shader transforms light positions and view direction into tangent space before the fragment shader raymarches the height map. Sub-layer interpolation weights the UV estimate between the last two sampled depth boundaries, eliminating banding at low layer counts.

Ping-pong Gaussian blur — Horizontal and vertical 1D passes alternate across 10 iterations by binding the other ping-pong FBO each pass. The firstIteration flag routes the first blur pass to read from the brightness-extracted output rather than an uninitialized buffer. The !horizontal index at the final glBindTexture correctly identifies the last-written buffer regardless of pass-count parity.

Wall-tangent direction — Player movement perpendicular to a wall surface uses Vector3.Cross(wallNormal, up) for the horizontal tangent. The sign is resolved by comparing the player’s current forward against both tangent directions — picking the closer one handles all wall angles without left/right flags.