Performance: SDL_Surface vs SDL_Renderer

The performance difference between rendering with SDL_Surface (and SDL_UpdateWindowSurface()) and SDL_Renderer (and SDL_RenderPresent()) is typically significant, with SDL_Renderer being considerably faster for most graphical tasks common in games and real-time applications.

Here's a breakdown of why:

SDL_Surface / SDL_UpdateWindowSurface() - CPU Bound

• Pixel Manipulation: Functions like SDL_FillRect, SDL_BlitSurface, and SDL_LoadBMP operate directly on pixel data stored in system RAM (CPU memory). Every pixel modification involves the CPU calculating and writing the new color value.
• Software Rendering: This is essentially software rendering. The speed is limited by your CPU's processing power and memory bandwidth.
• Data Transfer: SDL_UpdateWindowSurface() needs to copy the entire surface's pixel data from CPU RAM to the graphics card's memory (or an intermediate buffer) so it can be displayed. This data transfer can be a bottleneck, especially for large windows or high resolutions.
• Limited Effects: Implementing complex effects like rotation, scaling with filtering, transparency blending, or shaders is difficult and slow in software on the CPU.

Use Cases: Best suited for very simple graphics, applications where hardware acceleration isn't available or desired, or tasks involving direct pixel manipulation for non-real-time purposes.

SDL_Renderer / SDL_RenderPresent() - GPU Accelerated

• Hardware Acceleration: SDL_Renderer acts as an abstraction layer over hardware-accelerated graphics APIs like DirectX (Windows), OpenGL (Cross-platform), Metal (macOS/iOS). It leverages the power of the Graphics Processing Unit (GPU).
• GPU Operations: GPUs are highly specialized processors designed for parallel graphics tasks. Operations like clearing the screen, drawing textured rectangles (SDL_RenderCopy), drawing geometric primitives (SDL_RenderDrawRect), and handling blending are executed extremely quickly by the GPU hardware.
• Efficient Data Handling: Textures (SDL_Texture) used with renderers typically reside in the GPU's dedicated video memory (VRAM). Rendering involves the GPU manipulating its own memory, which is much faster than transferring large amounts from CPU RAM each frame. SDL_RenderPresent() often just involves telling the GPU to swap internal buffers, a very fast operation.
• Advanced Features: Renderers make it easy to perform hardware-accelerated scaling, rotation, blending, and potentially use shaders (depending on the backend) for advanced visual effects with minimal performance impact compared to CPU implementations.

Use Cases: The standard choice for games, simulations, multimedia applications, or any graphical application requiring smooth animation, high frame rates, complex scenes, or visual effects.

Performance Comparison Summary

Conclusion

For almost any application involving animation, multiple sprites, scrolling, or visual effects, the SDL_Renderer API will drastically outperform the SDL_Surface API.

The ability to offload rendering tasks to the specialized GPU hardware provides orders of magnitude speed improvements compared to performing those same tasks pixel-by-pixel on the CPU and then copying the result.

While SDL_Surface might seem simpler initially, the performance limitations become apparent very quickly as graphical complexity increases.