Commit graph

48513 commits

Author SHA1 Message Date
Jordan Justen
6cf3034ba7 mesa osmesa/x11: fix build error introduced in 4bea4cb9
Fixes https://bugs.freedesktop.org/show_bug.cgi?id=58380

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
2012-12-17 08:55:41 -08:00
Roland Scheidegger
3d14b25030 gallivm: fix texel fetch for array textures (2)
a460aea3f1 wasn't entirely correct,
since all coords are already ints hence need to skip the iround.
Passes piglit texelFetch with sampler1DArray/sampler2DArray.

Reviewed-by: Dave Airlie <airlied@redhat.com>
2012-12-17 11:50:27 +01:00
Jordan Justen
1358f3a905 mesa: assert if driver did not compute the version
Make sure drivers initialize the version before:
 * _mesa_initialize_exec_table is called
 * _mesa_initialize_exec_table_vbo is called
 * A context is made current

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:28 -08:00
Jordan Justen
075f8722ab mesa: don't initialize VBO vtxfmt in _vbo_CreateContext
The driver should call _mesa_initialize_vbo_vtxfmt after
computing the context version.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:28 -08:00
Jordan Justen
53ee3959f2 mesa: don't initialize exec dispatch tables in _mesa_initialize_context
Drivers must compute the context version, and then call
_mesa_initialize_exec_table themselves.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:27 -08:00
Jordan Justen
d5d1f10955 mesa dispatch_sanity: call new functions to initialize exec table
In a future patch the exec functions will no longer set up
by _mesa_initialize_context and _vbo_CreateContext.

Therefore we must call _mesa_initialize_exec_table and
_mesa_initialize_exec_table_vbo.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:27 -08:00
Jordan Justen
4bea4cb9fd drivers: compute version and then initialize exec table
This change forces the context version to be computed before
initilizing the exec dispatch tables.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:27 -08:00
Jordan Justen
0924f4e90c vbo: add _mesa_initialize_vbo_vtxfmt
This function initializes the exec/save dispatch tables
for VBO vtxfmt.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:27 -08:00
Jordan Justen
d440149538 mesa: separate exec allocation from initialization
In glapi/gl_genexec.py:
* Remove _mesa_alloc_dispatch_table call

In glapi/gl_genexec.py and api_exec.h:
* Rename _mesa_create_exec_table to _mesa_initialize_exec_table

In context.c:
* Call _mesa_alloc_dispatch_table instead of _mesa_create_exec_table
* Call _mesa_initialize_exec_table (this is temporary)

Once all drivers have been modified to call
_mesa_initialize_exec_table, then the call to
_mesa_initialize_context can be removed from context.c.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-16 15:30:27 -08:00
Dave Airlie
fa5078c255 r600g: fixup offset types for printing
This allows the debug code to at least show the sign properly.

Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-12-16 10:36:42 +00:00
Henri Verbeet
cf358a2b42 gallium/u_blitter: Remove the overlapped blit assert from util_blitter_blit_generic().
This is used by st_BlitFramebuffer() / r600_blit(), and ARB_fbo allows
overlapped blits, even though the result is undefined. No piglit regressions
on r600g / CYPRESS.

Signed-off-by: Henri Verbeet <hverbeet@gmail.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
2012-12-16 11:13:20 +01:00
Dave Airlie
a9abaaafd8 glsl_parser_extras.cpp: fixup gl vs mem contexts again.
This should fix:
https://bugs.freedesktop.org/show_bug.cgi?id=58039

Tested-by: Darxus on bug 58039
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-12-16 17:30:08 +10:00
Kenneth Graunke
4f91f8dd60 i965: Move BRW_MAX_GRF and similar defines to brw_reg.h.
These don't really belong in brw_structs.h.

Reviewed-by: Eric Anholt <eric@anholt.net>
2012-12-15 13:40:16 -08:00
Kenneth Graunke
1db1283563 i965: Split struct brw_reg out from brw_eu.h into its own header.
struct brw_instruction and the related instruction emitting code won't
be useful on Gen8+, as the instruction encoding changed.  However, the
struct brw_reg code is still extremely valuable.

While we're at it, fix up some style points:
- s/GLuint/unsigned/g
- s/GLint/int/g
- s/GLshort/int16_t/g
- s/GLushort/uint16_t/g
- s/INLINE/inline/g
- Replace tabs with spaces
- Put return types on a separate line from the function name/parameters
- Remove trailing whitespace
- Remove extraneous whitespace around function parameters

Reviewed-by: Eric Anholt <eric@anholt.net>
2012-12-15 13:40:09 -08:00
Dave Airlie
39fa4c0a58 st/mesa: add texture buffer object rgb32 support.
This checks if the pipe driver can support RGB32 formats.

Reviewed-by: Marek Olšák <maraeo@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-12-16 06:55:39 +10:00
Dave Airlie
1b62c326ea mesa: add support for ARB_texture_buffer_object_rgb32
This adds the extensions + the tex buffer support for checking
the formats.

There is a piglit test enhancement sent to that list.

Reviewed-by: Marek Olšák <maraeo@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-12-16 06:55:33 +10:00
Dave Airlie
7d7a549fa0 glsl: avoid using gl context as a memory context
Not sure what was going on here, but running piglit with debug builds
might be a good plan :-)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-12-15 15:29:49 +10:00
Ian Romanick
b23e92dbe7 i965: Add missing autoconf bits so test_vec4_register_coalesce will build
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Eric Anholt <eric@anholt.net>
2012-12-14 18:44:18 -08:00
Eric Anholt
c9e48e5b08 i965: Generalize VS compute-to-MRF for compute-to-another-GRF, too.
No statistically significant performance difference on glbenchmark 2.7
(n=60).  It reduces cycles spent in the vertex shader by 3.3% +/- 0.8%
(n=5), but that's only about .3% of all cycles spent according to the
fixed shader_time.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 16:06:35 -08:00
Eric Anholt
471af25fc5 i965/vs: Extend opt_compute_to_mrf to handle limited "reswizzling"
The way our visitor works, scalar expression/swizzle results that get
stored in channels other than .x will have an intermediate MOV from
their result in the .x channel to the real .y (or whatever) channel, and
similarly for vec2/vec3 results.

By knowing how to adjust DP4-type instructions for optimizing out a
swizzled MOV, we can reduce instructions in common matrix multiplication
cases.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 16:06:30 -08:00
Eric Anholt
a76a03f437 i965/vs: Add a unit test for opt_compute_to_mrf().
The compute-to-mrf code is really twitchy, and it's hard to construct
GLSL testcases for it.  This unit test is also really hard to work with
(for example, if your instruction is removed by dead code elimination,
you end up inspecting something irrelevant), but I did use it for
debugging some of the commits to follow.

I called it test_vec4_register_coalesce because the compute-to-mrf code
is about to morph into that.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 16:06:01 -08:00
Eric Anholt
7171c45d3a i965/fs: Drop an unnecessary _safe on a list walk.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 16:05:57 -08:00
Eric Anholt
78ce522932 i965/fs: Add a note explaining a detail of register_coalesce_2().
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 16:05:48 -08:00
Eric Anholt
7baf9198b2 i965: Also consider HALTs a potential block end.
The final halt of the fragment shader turns off the remaining channels,
then jumps such that everything is turned back on.  So, we can have our
last ENDIF of the shader point at that directly.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:45:26 -08:00
Kenneth Graunke
2702202290 i965: Jump to the end of the next outer conditional block on ENDIFs.
From the Ivybridge PRM, Volume 4, Part 3, section 6.24 (page 172):

"The endif instruction is also used to hop out of nested conditionals by
 jumping to the end of the next outer conditional block when all
 channels are disabled."

Also:
"Pseudocode:
 Evaluate(WrEn);
 if ( WrEn == 0 ) {  // all channels false
   Jump(IP + JIP);
 }"

First, ENDIF re-enables any channels that were disabled because they
didn't match the conditional.  If any channels are active, it proceeds
to the next instruction (IP + 16).  However, if they're all disabled,
there's no point in walking through all of the instructions that have no
effect---it can jump to the next instruction that might re-enable some
channels (an ELSE, ENDIF, or WHILE).

Previously, we always set JIP on ENDIF instructions to 2 (which is
measured in 8-byte units).  This made it do Jump(IP + 16), which just
meant it would go to the next instruction even if all channels were off.

It turns out that walking over instructions while all the channels are
disabled like this is worse than just instruction dispatch overhead: if
there are texturing messages, it still costs a couple hundred cycles to
not-actually-read from the texture results.

This patch finds the next instruction that could re-enable channels and
sets JIP accordingly.

Reviewed-by: Eric Anholt <eric@anholt.net>
2012-12-14 15:42:34 -08:00
Chris Forbes
2f7f095a80 i965: expose ARB_texture_cube_map_array
V3: Put enable in an existing block rather than making a new
one for no good reason.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:51 -08:00
Eric Anholt
380fc562b3 i965/fs: Fix setup for textureGrad(samplerCubeArray, coord, dPdx, dPdy)
Caught by tex_grad-01.frag.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:48 -08:00
Eric Anholt
3c56063354 i965/fs: Move the failure for gen7 16-wide intdiv to emit_math().
The cube map array code adds another caller of emit_math(), which
needs this check.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:43 -08:00
Chris Forbes
d2dbba8755 i965: fs: Add fixup for textureSize on Gen6/7
V2: Moved up into emit(ir_texture *) to avoid duplication and fix
ordering for Gen7; Gen6 math quirks moved into previous patches.

Tested on Gen6 only; passes all the cube_map_array piglits.

V3: Fixed weird whitespace
V4: Use sampler->type; otherwise broken on arrays of samplers.
v5: Minor style fixes (by anholt)

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:39 -08:00
Chris Forbes
6e34723ac9 i965: fs: fix gen6+ math operands in one place
V4: Fix various style nits as pointed out by Eric, and expand IMM
    operands on both Gen6 and Gen7.
v5: minor style nits (by anholt)

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:35 -08:00
Chris Forbes
f6a3fda25d i965: vs: Add fixup for textureSize with cube array samplers
V3: Fixed weird whitespace
V4: Use sampler's type rather than variable's type; otherwise broken
    with arrays of samplers. (Thanks Eric)
v5: Fix a couple more style nits (by anholt)

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:31 -08:00
Chris Forbes
1cb57ea493 i965/vs: Fix gen6+ math operand quirks in one place
This causes immediate values to get moved to a temp on gen7, which is needed
for an upcoming change but hadn't happened in the visitor until then.

v2: Drop gen > 7 checks (doesn't exist), and style-fix comments (changes by
    anholt).

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:28 -08:00
Chris Forbes
0cda3382a6 i965: Add various plumbing for cubemap arrays
V4: Fixed style nits

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:26:12 -08:00
Eric Anholt
2cae9f2d4a i965/fs: Add empirically-determined instruction latencies for gen7.
v2: Actually switch on the other math instructions mentioned in the
    comment.
v3: Add timing data for textureSize(), and clean up some long comment
    lines.

Testing shader_time of fs16 shaders on a few frames of various apps:
nexuiz improved by 2.9% +/- 1.5% (n=10)
no difference on GLB2.5 (n=36, outliers removed)
no difference on GLB2.7 (n=25)
etqw improved by 2.6% +/- 2.2% (n=25)
no difference on lightsmark (n=25)

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:18:22 -08:00
Eric Anholt
4df1e18864 i965/fs: Fix the clock increment in scheduling.
I've tested this to be true with various ALU ops on gen7 (with the
exception of MADs, which go at either 3 or 4 cycles per dispatch).

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:18:14 -08:00
Eric Anholt
6255fc7426 i965/fs: Move the old gen4 bspec-based scheduling info to a helper func.
For gen7 everything changes, and we have actual information on latency.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:18:10 -08:00
Eric Anholt
461a29783a i965/fs: Set up gen7 UBO loads as sends from GRFs.
This gives the instruction scheduler a chance to schedule between the
loads, whereas before it was restricted due to the dependencies between
the MRFs for setting them up.

For one shader in gles3conform, it goes from getting stuck in register
allocation for as long as anybody's bothered to leave it running down
to 23 seconds, thanks to the LIFO scheduling.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:18:05 -08:00
Eric Anholt
456dbcc337 i965/fs: Before reg alloc, schedule instructions to reduce live ranges.
This came from an idea by Ben Segovia.  16-wide pixel shaders are very
important for latency hiding on i965, so we want to try really hard to
get them.  If scheduling an instruction makes some set of instructions
available, those are probably the ones that make the instruction's
result dead.  By choosing those first, we'll have a tendency to reduce
the amount of live data as opposed to creating more.

Previously, we were sometimes getting this behavior out of the
scheduler, which was what produced the scheduler's original performance
wins on lightsmark.  Unfortunately, that was mostly an accident of the
lame instruction latency information that I had, which made it
impossible to fix the actual scheduling for performance.  Now that we've
fixed the scheduling for setup for register allocation, we can safely
update the latency parameters for the final schedule.

In shader-db, we lose 37 16-wide shaders, but gain 90 new ones.  4
shaders that were spilling change how many registers spill, for a
reduction of 70/3899 instructions.

v2: Simplify the new loop.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:17:59 -08:00
Eric Anholt
ba864bfcfa i965/fs: Add some optional debug printfs to scheduling.
Seeing when instructions become available to schedule is really useful.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:17:55 -08:00
Eric Anholt
7a9f940cab i965/fs: Schedule instructions both before and after register allocation.
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
2012-12-14 15:17:41 -08:00
Eric Anholt
1315f3b4b3 i965: Make sure that the shader_time report at context destroy happens.
Otherwise, you end up with some report from within a second of context
destroy, which is now what you really want for testing the impact of
changes
2012-12-14 15:05:10 -08:00
Eric Anholt
81c247404a i965: Print a total time for the different shader stages.
Sometimes I've got a patch for a performance optimization that's not
showing a statistically significant performance difference on reported
FPS, but still seems like a good idea because it ought to reduce time
spent in the shader.  If I can see the total number of cycles spent in
the shader stage being optimized, it may show that the patch is still
worthwhile (or point out that it's actually broken in some way).
2012-12-14 15:05:10 -08:00
Eric Anholt
f74560f3fb i965: Scale shader_time to compensate for resets.
Some shaders experience resets more than others, which skews the numbers
reported.  Attempt to correct for this by linearly scaling according to
the number of resets that happen.

Note that will not be accurate if invocations of shaders have varying
times and longer invocations are more likely to reset.  However, this
should at least be better than the previous situation.
2012-12-14 15:05:10 -08:00
Eric Anholt
338b5f887d i965: Adjust the split between shader_time_end() and shader_time_write().
I'm about to emit other kinds of writes besides time deltas, and it
turns out with the frequency of resets, we couldn't really use the old
time delta write() function more than once in a shader.
2012-12-14 15:05:10 -08:00
Paul Berry
ca7e891e8a glsl/linker: Pack between varyings.
This patch implements varying packing between varyings.

Previously, each varying occupied components 0 through N-1 of its
assigned varying slot, so there was no way to pack two varyings into
the same slot.  For example, if the varyings were a float, a vec2, a
vec3, and another vec2, they would be stored as follows:

 <----slot1----> <----slot2----> <----slot3----> <----slot4---->  slots
  *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 flt  x   x   x  <vec2->  x   x  <--vec3--->  x  <vec2->  x   x   varyings

(Each * represents a varying component, and the "x"s represent wasted
space).

This change packs the varyings together to eliminate wasted space
between varyings, like so:

 <----slot1----> <----slot2----> <----slot3----> <----slot4---->  slots
  *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 <vec2-> <vec2-> flt <--vec3--->  x   x   x   x   x   x   x   x   varyings

Note that we take advantage of the sort order introduced in previous
patches (vec4's first, then vec2's, then scalars, then vec3's) to
minimize how often a varying is "double parked" (split across varying
slots).

Reviewed-by: Eric Anholt <eric@anholt.net>

v2: Skip varying packing if ctx->Const.DisableVaryingPacking is true.
2012-12-14 10:51:21 -08:00
Paul Berry
df87722bec glsl/linker: Pack within compound varyings.
This patch implements varying packing within varyings that are
composed of multiple vectors of size less than 4 (e.g. arrays of
vec2's, or matrices with height less than 4).

Previously, such varyings used up a full 4-wide varying slot for each
constituent vector, meaning that some of the components of each
varying slot went unused.  For example, a mat4x3 would be stored as
follows:

 <----slot1----> <----slot2----> <----slot3----> <----slot4---->  slots
  *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 <-column1->  x  <-column2->  x  <-column3->  x  <-column4->  x   matrix

(Each * represents a varying component, and the "x"s represent wasted
space).  In addition to wasting precious varying components, this
layout complicated transform feedback, since the constituents of the
varying are expected to be output to the transform feedback buffer
contiguously (e.g. without gaps between the columns, in the case of a
matrix).

This change packs the constituents of each varying together so that
all wasted space is at the end.  For the mat4x3 example, this looks
like so:

 <----slot1----> <----slot2----> <----slot3----> <----slot4---->  slots
  *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 <-column1-> <-column2-> <-column3-> <-column4->  x   x   x   x   matrix

Note that matrix columns 2 and 3 now cross a boundary between varying
slots (a characteristic I call "double parking" of a varying).

We don't bother trying to eliminate the wasted space at the end of the
varying, since the patch that follows will take care of that.

Since compiler back-ends don't (yet) support this packed layout, the
lower_packed_varyings function is used to rewrite the shader into a
form where each varying occupies a full varying slot.  Later, if we
add native back-end support for varying packing, we can make this
lowering pass optional.

Reviewed-by: Eric Anholt <eric@anholt.net>

v2: Skip varying packing if ctx->Const.DisableVaryingPacking is true.
2012-12-14 10:51:18 -08:00
Paul Berry
4bb8661b1b gallium: Disable varying packing on hardware with <=8 texture indirections.
In practice this will disable varying packing on R300, R400, i915g,
and nv30.

Reviewed-by: Marek Olšák <maraeo@gmail.com>
2012-12-14 10:51:10 -08:00
Paul Berry
6ee500cfd2 mesa: Add an option so driver can opt out of varying packing.
On hardware that supports a limited number of texture indirections,
varying packing will comsume an extra texture indirection, since ALU
operations are needed in the fragment shader to unpack the varyings
before any texturing can be done.

This patch introduces a new driver option,
ctx->Const.DisableVaryingPacking, which can be used by a driver to opt
out of varying packing if the extra texture indirection is costly
enough to outweigh the advantages of packing varyings.

Reviewed-by: Marek Olšák <maraeo@gmail.com>
2012-12-14 10:49:32 -08:00
Paul Berry
1745a4d751 glsl: Add a lowering pass for packing varyings.
This lowering pass generates GLSL code that manually packs varyings
into vec4 slots, for the benefit of back-ends that don't support
packed varyings natively.

No functional change--the lowering pass is not yet used.

Reviewed-by: Eric Anholt <eric@anholt.net>

v2: Don't use ir_hierarchical_visitor--just loop over instructions
directly.  Also, make the names of the packed varyings include the
names of the original varyings that were packed into them.
2012-12-14 10:49:21 -08:00
Paul Berry
f3993107f0 glsl/linker: Sort varyings by packing class, then vector size.
This patch paves the way for varying packing by adding a sorting step
before varying assignment, which sorts the varyings into an order that
increases the likelihood of being able to find an efficient packing.

First, varyings are sorted into "packing classes" by considering
attributes that can't be mixed during varying packing--at the moment
this includes base type (float/int/uint/bool) and interpolation mode
(smooth/noperspective/flat/centroid), though later we will hopefully
be able to relax some of these restrictions.  The number of packing
classes places an upper limit on the amount of space that must be
wasted by varying packing, since in theory a shader might nave 4n+1
components worth of varyings in each of m packing classes, resulting
in 3m components worth of wasted space.

Then, within each packing class, varyings are sorted by vector size,
with vec4's coming first, then vec2's, then scalars, and then finally
vec3's.  The motivation for this order is that it ensures that the
only vectors that might be "double parked" (with part of the vector in
one varying slot and the remainder in another) are vec3's.

Note that the varyings aren't actually packed yet, merely placed in an
order that will facilitate packing.

Reviewed-by: Eric Anholt <eric@anholt.net>
2012-12-14 10:49:12 -08:00