Why Alternate Frame Rendering Died in DirectX 12

Alternate Frame Rendering (AFR) was long the primary technique used by multi-GPU setups—such as NVIDIA SLI and AMD CrossFire—to boost gaming performance by alternating frame generation across multiple graphics cards. However, while effective in older DirectX 9 and 11 environments, AFR has largely disappeared from modern gaming. This article examines the fundamentals of Alternate Frame Rendering and explains how the architectural design of DirectX 12, coupled with modern rendering pipelines like temporal anti-aliasing and ray tracing, rendered AFR obsolete.

What Is Alternate Frame Rendering?

Alternate Frame Rendering is a multi-GPU processing method where two or more graphics cards share the workload on a frame-by-frame basis. Instead of splitting a single frame across multiple chips, the GPUs alternate sequentially. For example, in a two-GPU system:

  • GPU 1 renders odd frames (1, 3, 5, 7...).
  • GPU 2 renders even frames (2, 4, 6, 8...).

On paper, this approach delivers a near-linear scaling of frame rates because each card operates with full autonomy over its assigned frame. In older game engines, where each frame was rendered in isolation without relying on data from the preceding frame, AFR was the most efficient way to maximize multi-card setups.

Why AFR Is Rarely Used in Modern DirectX 12 Titles

Despite its past success, AFR is virtually nonexistent in contemporary DirectX 12 games due to fundamental shifts in game engine design, API architecture, and hardware economics.

1. Inter-Frame Dependencies and Temporal Rendering

The single biggest technical hurdle for AFR is the rise of temporal graphics techniques. Modern game engines rarely render frames in isolation; instead, they heavily depend on the data of the previous frame. Features such as:

  • Temporal Anti-Aliasing (TAA): Blends color and geometry data from prior frames to smooth edges.
  • Temporal Upscaling (DLSS, FSR, XeSS): Analyzes historical frames and motion vectors to reconstruct high-resolution images.
  • Screen-Space Reflections and Ambient Occlusion: Samples previous visual buffers to calculate lighting.

Under AFR, GPU 2 needs the visual data generated by GPU 1 to complete its frame. To share this data, the output must be copied across the PCIe bus or bridge interconnect. This transfer introduces severe bandwidth bottlenecks and latency, which negates any performance gains that a second GPU would provide.

2. Micro-Stutter and Input Latency

AFR has an inherent architectural flaw: frame delivery variance. Because two separate GPUs rarely finish rendering frames at identical speeds due to fluctuating scene complexity, frames often arrive at the display unevenly. This results in micro-stuttering, where the reported frame rate may be high, but the gameplay feels choppy.

Additionally, because a frame rendered by the second GPU must wait in a queue to be presented after the first GPU's frame, AFR inherently increases input latency.

3. The Shift to Explicit Multi-GPU in DirectX 12

In DirectX 11, multi-GPU support was managed largely through graphics drivers maintained by NVIDIA and AMD. The GPU vendors spent significant resources creating custom game profiles to resolve synchronization issues.

DirectX 12 completely changed this paradigm by introducing low-level access to the hardware. With DirectX 12’s Explicit Multi-Adapter (EMA) mode, control over multi-GPU coordination was shifted entirely to the game developers. Given that multi-GPU users make up a fraction of a percent of all PC gamers, developers can rarely justify the immense development cost and engineering hours required to manually synchronize memory and execution queues across multiple adapters.

4. Alternative Techniques Replaced AFR

Where multi-GPU implementations exist in professional software or specialized modern games, developers prefer alternative methods over AFR:

  • Split Frame Rendering (SFR): Dividing a single frame dynamically across GPUs based on workload.
  • Asynchronous Compute Offloading: Designating one GPU strictly for compute-heavy tasks like physics, particle simulation, or ray-traced audio, while the primary GPU handles rasterization.

Ultimately, between the industry-wide adoption of temporal rendering pipelines and the end of driver-level SLI and CrossFire support, Alternate Frame Rendering has become incompatible with modern real-time graphics pipelines.