Looking at online specifications for the Power Macintosh 8500, I was able to find few details on its graphics capabilities beyond quantity of VRAM and supported color depths, refresh rates, and resolutions:

Did it have any hardware acceleration of 2D graphics at all like that which would be seen later in the Power Macintosh 9600 with the IXMICRO TwinTurbo 128? For example, were there any specialized units for screen-to-screen copies, bresenham lines, or raster operations?

If not, was software rendering/blitting in general good enough for a responsive windowing system with resolutions and hardware common in the mid-90s? How necessary were windows accelerators to run user interfaces smoothly? Given that, according to Wikipedia, the 8500 was "billed as a high-end graphics computer", I would assume that if software rendering was good enough for its use case, it would have been good enough for most.

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    PowerMacs coincede more with the advent of 3D accelerators. 2D acceleration fits mid-late 68k Macs time-wise. (Meaning: When PowerPC Macs arrived, there was already 3D acceleration) – tofro Feb 10 at 9:02
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    @tofro in that regard Macs were lagging quite behind ... in fact they were with most hardware until rather recently, i.e. until they started to use standard Wintel-Hardware. – Raffzahn Feb 10 at 11:52
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    “Responsive windowing system” — bear in mind that in the mid-nineties, dragging with full window contents was a rare feature, and window operations used outlines... – Stephen Kitt Feb 10 at 13:16
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    The first PowerMacs predate any 3d accelerators, the 8500 predates any useful ones; the laptops had 3d acceleration before the year 2000; OS X had a full compositing desktop by 2002 — four years ahead of Compiz and Windows Vista. – Tommy Feb 11 at 3:06

On the objective stuff, per Apple's 7500/8500 hardware devnotes, Page 20:

The video subsystem is implemented by the following ICs:

■ Chaos, a custom IC that provides data bus buffering between the video subsystem and the processor bus

■ Control, a custom IC that provides addressing and control for the video subsystem

■ RaDACal, a high-performance digital-to-analog converter (DAC) used for the video stream to the monitor

■ Sixty6, an RGB-to-YUV converter and convolver for the second video output stream (on the Power Macintosh 8500 computer only)

■ a 7187 digital video encoder (DENC) for the second video output stream (on the Power Macintosh 8500 computer only)

■ an 8758 analog-to-digital converter (ADC) for the video input stream

■ a 7196 digital video decoder and scaler IC (DESC) for the video input stream

■ Plan B, a DMA controller for video input data from the 7196 DESC IC

Elsewhere in that section only very limited forms of hardware acceleration are hinted at:

The RaDACal IC also ... supports the hardware cursor.

The video input feature is implemented by the 8758 video ADC IC ... video data can be stored either in the video display buffer (VRAM) or in an offscreen pixel map in main memory. Video data transfers are DMA transfers and are controlled by a DBDMA engine in the Plan B IC.

When video input data is sent to the display buffer, it can be clipped with a 1-bit-per-pixel clip mask using the DBDMA read channel. ...

When video input data is stored in a pixel map in main memory, software can perform any required clipping and blending by using the CopyBits routine in QuickDraw when moving the pixel map to a visible region of the display.

So it appears as if there was a fast hardware path for dealing with video input (in the AV sense), including depositing it at an appropriate on- or off-screen destination and clipping it if it is sent on-screen. It also seems that any graphics, once in memory, are manipulated in software using the standard Apple calls.

I therefore think the answer to your question is that no hardware acceleration was provided for ordinary 2d graphics.

On the subjective, software rendering was indeed more than good enough for the typical resolutions and usages of the mid-'90s, on both the PC and the Mac — to the point that many of the pre-3dfx/PowerVR 3d accelerators were derided for doing a worse job than software rendering, e.g. from 2003:

It may seem hard to believe now, but ten years ago, S3 was the market leader for 2D-only GPUs. But as the 3D revolution gathered steam in 1996, it became clear that S3’s ViRGE GPU wasn’t going to allow S3 to maintain its dominant market position. In fact, the ViRGE became known as a “3D decelerator”.

1996 is the year after the introduction of the 8500.

If you want easy YouTube points of reference then check out the Apple Pippin — it has a PowerPC 601, substantially slower than the 604 in the 8500 — and no video or audio acceleration whatsoever but manages to throw around mild 3d scenes at TV resolutions; suffice to say that at desktop resolutions a 604 is more than a match for the more sedate world of that era's desktop 2d.

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