Module Name: src
Committed By: macallan
Date: Wed Jan 29 15:35:22 UTC 2025
Modified Files:
src/sys/dev/ic: summitreg.h
Log Message:
comment on what I've found out about alpha blending on the FX4
NFC
To generate a diff of this commit:
cvs rdiff -u -r1.15 -r1.16 src/sys/dev/ic/summitreg.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/dev/ic/summitreg.h
diff -u src/sys/dev/ic/summitreg.h:1.15 src/sys/dev/ic/summitreg.h:1.16
--- src/sys/dev/ic/summitreg.h:1.15 Mon Jan 27 11:38:39 2025
+++ src/sys/dev/ic/summitreg.h Wed Jan 29 15:35:22 2025
@@ -1,4 +1,4 @@
-/* $NetBSD: summitreg.h,v 1.15 2025/01/27 11:38:39 macallan Exp $ */
+/* $NetBSD: summitreg.h,v 1.16 2025/01/29 15:35:22 macallan Exp $ */
/*
* Copyright (c) 2024 Michael Lorenz
@@ -164,7 +164,14 @@
#define IBO_MIN 0x600
#define IBO_MAX 0x700
-/* the blend functions seem to be: */
+/*
+ * here are the blend functions I identified
+ * apparently the upper byte in 32bit mode is not implemented on FX2/4/6, and
+ * neither is any blend mode that takes the colour value from CBR
+ * so no blending with screen-to-screen blits, alpha will always read zero
+ * the only ways to actually use alpha blending is with fills ( the alpha part
+ * of the FG register is used ) and BINC writes, or when using constant alpha
+ */
#define IBO_ZERO 0
#define IBO_ONE 1
#define IBO_SRC 4 /* src alpha */
