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James Dansereau
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Public-copy language pass, homepage restructure and Documentation rename, 404 page, dead-anchor and permalink fixes, release-gate sign-off, and the pre-release review fixes of the 2026-10-05 batch (probe-doc drift, build-path hygiene, verify.sh and capture safety). Refs: D533 D534
39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
---
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title: The software RSP
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description: How the GoldenEye 007 PC port emulates the N64's Reality Signal Processor (the graphics coprocessor) in software and bypasses the RDP.
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date: '2026-10-05'
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modified_time: '2026-10-05'
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---
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## The software RSP
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On the N64, the **Reality Signal Processor (RSP)** is the graphics
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coprocessor. The R4300 CPU builds a list of graphics commands each frame
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(the **GBI display list**); the RSP runs a "fast3d" microcode that turns
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those commands into **RDP** (rasterizer) commands, which the RDP turns into
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pixels.
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The port does two things to that pipeline:
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- **It emulates the RSP in software.** `port/fast3d/` (~7,000 lines of C++,
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adapted from the Perfect Dark port) *is* the RSP: it interprets the GBI
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display list the game builds and, instead of emitting RDP commands, emits
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**OpenGL** calls directly.
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- **It bypasses the RDP entirely** — there is no rasterizer to emulate,
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because the software RSP talks straight to the GPU.
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The game's own R4300 code runs natively and is unaware of the difference: it
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builds display lists and "starts the RSP" exactly as it would on hardware. A
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replacement scheduler (`pdsched.c`) catches the "start the RSP" call and runs
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the software RSP on the render thread.
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GoldenEye's custom commands are handled by the same interpreter: the packed
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four-triangle `G_TRI4` command and the fade/blend **color-combiner** modes
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(compiled on the fly from the N64's combiner equation to a GLSL shader by
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`gfx_cc.cpp`). The N64's own RSP microcode (`rsp/graphics/gmain.s`) is not
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run on PC but is the reference the software RSP's command decoding is checked
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against.
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*More: [internals](internals.md) §2 (the reference architecture) and §5
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(GoldenEye-specific graphics work).*
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