The view is shifted 50% to the left in many OpenGL apps on ati video cards

[alexander@…]

This is a duplicate of ​https://bugs.freedesktop.org/show_bug.cgi?id=6046

The patch attached there fixes the problem only for r300 cards, and is thus incomplete. A workaround that works for all cards is to change the "make linux-dri" command in Mesa instructions to:

make OPT_FLAGS="-O2 -pipe -fno-strict-aliasing" linux-dri-x86

The important part is -fno-strict-aliasing.

[dnicholson@…]

I haven't given this much thought as I have an r200 card and these things work fine for me.

Alexander, do you think it's fine to add -fno-strict-aliasing for everything? Surely it can't hurt. This seems like an easy workaround.

[alexander@…]

That's even the workaround recommended by Mesa developers: "That said, there are still potential aliasing problems in the code, I'd suggest you compile with -fno-strict-aliasing for the time being."

[alexander@…]

If you were asking about "-fno-strict-aliasing for everything, not just Mesa", +1. The LiveCD already does this, because there were too many issues without this flag. Slirp (both standalone and as a part of qemu), MySQL, and Mesa come to mind, and the breakage is at runtime in all such cases.

[dnicholson@…]

Going to add -fno-strict-aliasing. I do agree with the use of linux-dri-x86 since the book only supports x86 and it adds a few nice things on top of the linux-dri target. Plus, anyone using a different arch following the book should be able to figure out how to substitute the correct config file. Here's the linux-dri-x86 config file:

# -*-makefile-*-
# Configuration for linux-dri: Linux DRI hardware drivers for XFree86 & others

include $(TOP)/configs/linux-dri

CONFIG_NAME = linux-dri-x86

# Unnecessary on x86, generally.
PIC_FLAGS =

# Add -m32 to CFLAGS:
ARCH_FLAGS = -m32

ASM_FLAGS = -DUSE_X86_ASM -DUSE_MMX_ASM -DUSE_3DNOW_ASM -DUSE_SSE_ASM
ASM_SOURCES = $(X86_SOURCES)
ASM_API = $(X86_API)

However, although '-O2 -pipe' are very safe CFLAGS, we don't set the optimization flags anywhere else in the book (that I know of). Instead, I'm plan to add this sed:

sed -i 's/^OPT_FLAGS  =.*/& -fno-strict-aliasing/' configs/linux-dri

Anyone who knows what they're doing can always override OPT_FLAGS at build time.

Comments on the change from the linux-dri target to the linux-dri-x86 target and the above sed?

[dnicholson@…]

Changed my mind on both things. I'm passing OPT_FLAGS="-O2 -fno-strict-aliasing" to the make command. This is the correct way to do things with make. And there are a couple other places in the book where we do things like this.

And I changed the target to linux-dri-x86. It adds a few nice flags that would probably added if a typical configure script is used. I mentioned the location to look for other targets if the arch isn't x86.

Fixed in r6324.