244 lines
12 KiB
C
244 lines
12 KiB
C
#ifndef QUAD_PIXEL_COMMUNICATION_H
|
|
#define QUAD_PIXEL_COMMUNICATION_H
|
|
|
|
///////////////////////////////// MIT LICENSE ////////////////////////////////
|
|
|
|
// Copyright (C) 2014 TroggleMonkey*
|
|
//
|
|
// Permission is hereby granted, free of charge, to any person obtaining a copy
|
|
// of this software and associated documentation files (the "Software"), to
|
|
// deal in the Software without restriction, including without limitation the
|
|
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
|
|
// sell copies of the Software, and to permit persons to whom the Software is
|
|
// furnished to do so, subject to the following conditions:
|
|
//
|
|
// The above copyright notice and this permission notice shall be included in
|
|
// all copies or substantial portions of the Software.
|
|
//
|
|
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
|
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
|
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
|
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
|
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
|
|
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
|
|
// IN THE SOFTWARE.
|
|
|
|
///////////////////////////////// DISCLAIMER /////////////////////////////////
|
|
|
|
// *This code was inspired by "Shader Amortization using Pixel Quad Message
|
|
// Passing" by Eric Penner, published in GPU Pro 2, Chapter VI.2. My intent
|
|
// is not to plagiarize his fundamentally similar code and assert my own
|
|
// copyright, but the algorithmic helper functions require so little code that
|
|
// implementations can't vary by much except bugfixes and conventions. I just
|
|
// wanted to license my own particular code here to avoid ambiguity and make it
|
|
// clear that as far as I'm concerned, people can do as they please with it.
|
|
|
|
///////////////////////////////// DESCRIPTION ////////////////////////////////
|
|
|
|
// Given screen pixel numbers, derive a "quad vector" describing a fragment's
|
|
// position in its 2x2 pixel quad. Given that vector, obtain the values of any
|
|
// variable at neighboring fragments.
|
|
// Requires: Using this file in general requires:
|
|
// 1.) ddx() and ddy() are present in the current Cg profile.
|
|
// 2.) The GPU driver is using fine/high-quality derivatives.
|
|
// Functions will give incorrect results if this is not true,
|
|
// so a test function is included.
|
|
|
|
|
|
///////////////////// QUAD-PIXEL COMMUNICATION PRIMITIVES ////////////////////
|
|
|
|
float4 get_quad_vector_naive(const float4 output_pixel_num_wrt_uvxy)
|
|
{
|
|
// Requires: Two measures of the current fragment's output pixel number
|
|
// in the range ([0, IN.output_size.x), [0, IN.output_size.y)):
|
|
// 1.) output_pixel_num_wrt_uvxy.xy increase with uv coords.
|
|
// 2.) output_pixel_num_wrt_uvxy.zw increase with screen xy.
|
|
// Returns: Two measures of the fragment's position in its 2x2 quad:
|
|
// 1.) The .xy components are its 2x2 placement with respect to
|
|
// uv direction (the origin (0, 0) is at the top-left):
|
|
// top-left = (-1.0, -1.0) top-right = ( 1.0, -1.0)
|
|
// bottom-left = (-1.0, 1.0) bottom-right = ( 1.0, 1.0)
|
|
// You need this to arrange/weight shared texture samples.
|
|
// 2.) The .zw components are its 2x2 placement with respect to
|
|
// screen xy direction (IN.position); the origin varies.
|
|
// quad_gather needs this measure to work correctly.
|
|
// Note: quad_vector.zw = quad_vector.xy * float2(
|
|
// ddx(output_pixel_num_wrt_uvxy.x),
|
|
// ddy(output_pixel_num_wrt_uvxy.y));
|
|
// Caveats: This function assumes the GPU driver always starts 2x2 pixel
|
|
// quads at even pixel numbers. This assumption can be wrong
|
|
// for odd output resolutions (nondeterministically so).
|
|
const float4 pixel_odd = frac(output_pixel_num_wrt_uvxy * 0.5) * 2.0;
|
|
const float4 quad_vector = pixel_odd * 2.0 - float4(1.0);
|
|
return quad_vector;
|
|
}
|
|
|
|
float4 get_quad_vector(const float4 output_pixel_num_wrt_uvxy)
|
|
{
|
|
// Requires: Same as get_quad_vector_naive() (see that first).
|
|
// Returns: Same as get_quad_vector_naive() (see that first), but it's
|
|
// correct even if the 2x2 pixel quad starts at an odd pixel,
|
|
// which can occur at odd resolutions.
|
|
const float4 quad_vector_guess =
|
|
get_quad_vector_naive(output_pixel_num_wrt_uvxy);
|
|
// If quad_vector_guess.zw doesn't increase with screen xy, we know
|
|
// the 2x2 pixel quad starts at an odd pixel:
|
|
const float2 odd_start_mirror = 0.5 * float2(ddx(quad_vector_guess.z),
|
|
ddy(quad_vector_guess.w));
|
|
return quad_vector_guess * odd_start_mirror.xyxy;
|
|
}
|
|
|
|
float4 get_quad_vector(const float2 output_pixel_num_wrt_uv)
|
|
{
|
|
// Requires: 1.) ddx() and ddy() are present in the current Cg profile.
|
|
// 2.) output_pixel_num_wrt_uv must increase with uv coords and
|
|
// measure the current fragment's output pixel number in:
|
|
// ([0, IN.output_size.x), [0, IN.output_size.y))
|
|
// Returns: Same as get_quad_vector_naive() (see that first), but it's
|
|
// correct even if the 2x2 pixel quad starts at an odd pixel,
|
|
// which can occur at odd resolutions.
|
|
// Caveats: This function requires less information than the version
|
|
// taking a float4, but it's potentially slower.
|
|
// Do screen coords increase with or against uv? Get the direction
|
|
// with respect to (uv.x, uv.y) for (screen.x, screen.y) in {-1, 1}.
|
|
const float2 screen_uv_mirror = float2(ddx(output_pixel_num_wrt_uv.x),
|
|
ddy(output_pixel_num_wrt_uv.y));
|
|
const float2 pixel_odd_wrt_uv = frac(output_pixel_num_wrt_uv * 0.5) * 2.0;
|
|
const float2 quad_vector_uv_guess = (pixel_odd_wrt_uv - float2(0.5)) * 2.0;
|
|
const float2 quad_vector_screen_guess = quad_vector_uv_guess * screen_uv_mirror;
|
|
// If quad_vector_screen_guess doesn't increase with screen xy, we know
|
|
// the 2x2 pixel quad starts at an odd pixel:
|
|
const float2 odd_start_mirror = 0.5 * float2(ddx(quad_vector_screen_guess.x),
|
|
ddy(quad_vector_screen_guess.y));
|
|
const float4 quad_vector_guess = float4(
|
|
quad_vector_uv_guess, quad_vector_screen_guess);
|
|
return quad_vector_guess * odd_start_mirror.xyxy;
|
|
}
|
|
|
|
void quad_gather(const float4 quad_vector, const float4 curr,
|
|
out float4 adjx, out float4 adjy, out float4 diag)
|
|
{
|
|
// Requires: 1.) ddx() and ddy() are present in the current Cg profile.
|
|
// 2.) The GPU driver is using fine/high-quality derivatives.
|
|
// 3.) quad_vector describes the current fragment's location in
|
|
// its 2x2 pixel quad using get_quad_vector()'s conventions.
|
|
// 4.) curr is any vector you wish to get neighboring values of.
|
|
// Returns: Values of an input vector (curr) at neighboring fragments
|
|
// adjacent x, adjacent y, and diagonal (via out parameters).
|
|
adjx = curr - ddx(curr) * quad_vector.z;
|
|
adjy = curr - ddy(curr) * quad_vector.w;
|
|
diag = adjx - ddy(adjx) * quad_vector.w;
|
|
}
|
|
|
|
void quad_gather(const float4 quad_vector, const float3 curr,
|
|
out float3 adjx, out float3 adjy, out float3 diag)
|
|
{
|
|
// Float3 version
|
|
adjx = curr - ddx(curr) * quad_vector.z;
|
|
adjy = curr - ddy(curr) * quad_vector.w;
|
|
diag = adjx - ddy(adjx) * quad_vector.w;
|
|
}
|
|
|
|
void quad_gather(const float4 quad_vector, const float2 curr,
|
|
out float2 adjx, out float2 adjy, out float2 diag)
|
|
{
|
|
// Float2 version
|
|
adjx = curr - ddx(curr) * quad_vector.z;
|
|
adjy = curr - ddy(curr) * quad_vector.w;
|
|
diag = adjx - ddy(adjx) * quad_vector.w;
|
|
}
|
|
|
|
float4 quad_gather(const float4 quad_vector, const float curr)
|
|
{
|
|
// Float version:
|
|
// Returns: return.x == current
|
|
// return.y == adjacent x
|
|
// return.z == adjacent y
|
|
// return.w == diagonal
|
|
float4 all = float4(curr);
|
|
all.y = all.x - ddx(all.x) * quad_vector.z;
|
|
all.zw = all.xy - ddy(all.xy) * quad_vector.w;
|
|
return all;
|
|
}
|
|
|
|
float4 quad_gather_sum(const float4 quad_vector, const float4 curr)
|
|
{
|
|
// Requires: Same as quad_gather()
|
|
// Returns: Sum of an input vector (curr) at all fragments in a quad.
|
|
float4 adjx, adjy, diag;
|
|
quad_gather(quad_vector, curr, adjx, adjy, diag);
|
|
return (curr + adjx + adjy + diag);
|
|
}
|
|
|
|
float3 quad_gather_sum(const float4 quad_vector, const float3 curr)
|
|
{
|
|
// Float3 version:
|
|
float3 adjx, adjy, diag;
|
|
quad_gather(quad_vector, curr, adjx, adjy, diag);
|
|
return (curr + adjx + adjy + diag);
|
|
}
|
|
|
|
float2 quad_gather_sum(const float4 quad_vector, const float2 curr)
|
|
{
|
|
// Float2 version:
|
|
float2 adjx, adjy, diag;
|
|
quad_gather(quad_vector, curr, adjx, adjy, diag);
|
|
return (curr + adjx + adjy + diag);
|
|
}
|
|
|
|
float quad_gather_sum(const float4 quad_vector, const float curr)
|
|
{
|
|
// Float version:
|
|
const float4 all_values = quad_gather(quad_vector, curr);
|
|
return (all_values.x + all_values.y + all_values.z + all_values.w);
|
|
}
|
|
|
|
bool fine_derivatives_working(const float4 quad_vector, float4 curr)
|
|
{
|
|
// Requires: 1.) ddx() and ddy() are present in the current Cg profile.
|
|
// 2.) quad_vector describes the current fragment's location in
|
|
// its 2x2 pixel quad using get_quad_vector()'s conventions.
|
|
// 3.) curr must be a test vector with non-constant derivatives
|
|
// (its value should change nonlinearly across fragments).
|
|
// Returns: true if fine/hybrid/high-quality derivatives are used, or
|
|
// false if coarse derivatives are used or inconclusive
|
|
// Usage: Test whether quad-pixel communication is working!
|
|
// Method: We can confirm fine derivatives are used if the following
|
|
// holds (ever, for any value at any fragment):
|
|
// (ddy(curr) != ddy(adjx)) or (ddx(curr) != ddx(adjy))
|
|
// The more values we test (e.g. test a float4 two ways), the
|
|
// easier it is to demonstrate fine derivatives are working.
|
|
// TODO: Check for floating point exact comparison issues!
|
|
float4 ddx_curr = ddx(curr);
|
|
float4 ddy_curr = ddy(curr);
|
|
float4 adjx = curr - ddx_curr * quad_vector.z;
|
|
float4 adjy = curr - ddy_curr * quad_vector.w;
|
|
bool ddy_different = any(bool4(ddy_curr.x != ddy(adjx).x, ddy_curr.y != ddy(adjx).y, ddy_curr.z != ddy(adjx).z, ddy_curr.w != ddy(adjx).w));
|
|
bool ddx_different = any(bool4(ddx_curr.x != ddx(adjy).x, ddx_curr.y != ddx(adjy).y, ddx_curr.z != ddx(adjy).z, ddx_curr.w != ddx(adjy).w));
|
|
return any(bool2(ddy_different, ddx_different));
|
|
}
|
|
|
|
bool fine_derivatives_working_fast(const float4 quad_vector, float curr)
|
|
{
|
|
// Requires: Same as fine_derivatives_working()
|
|
// Returns: Same as fine_derivatives_working()
|
|
// Usage: This is faster than fine_derivatives_working() but more
|
|
// likely to return false negatives, so it's less useful for
|
|
// offline testing/debugging. It's also useless as the basis
|
|
// for dynamic runtime branching as of May 2014: Derivatives
|
|
// (and quad-pixel communication) are currently disallowed in
|
|
// branches. However, future GPU's may allow you to use them
|
|
// in dynamic branches if you promise the branch condition
|
|
// evaluates the same for every fragment in the quad (and/or if
|
|
// the driver enforces that promise by making a single fragment
|
|
// control branch decisions). If that ever happens, this
|
|
// version may become a more economical choice.
|
|
float ddx_curr = ddx(curr);
|
|
float ddy_curr = ddy(curr);
|
|
float adjx = curr - ddx_curr * quad_vector.z;
|
|
return (ddy_curr != ddy(adjx));
|
|
}
|
|
|
|
#endif // QUAD_PIXEL_COMMUNICATION_H
|
|
|