michael@0: /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
michael@0:   * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:   * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:   * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: Texture2D InputTexture : register(t0);
michael@0: SamplerState InputSampler : register(s0);
michael@0: Texture2D GradientTexture : register(t1);
michael@0: SamplerState GradientSampler : register(s1);
michael@0: 
michael@0: cbuffer constants : register(b0)
michael@0: {
michael@0:     // Precalculate as much as we can!
michael@0:     float3 diff : packoffset(c0.x);
michael@0:     float2 center1 : packoffset(c1.x);
michael@0:     float A : packoffset(c1.z);
michael@0:     float radius1 : packoffset(c1.w);
michael@0:     float sq_radius1 : packoffset(c2.x);
michael@0:     float3x2 transform : packoffset(c3.x);
michael@0: }
michael@0: 
michael@0: float4 SampleRadialGradientPS(
michael@0:     float4 clipSpaceOutput  : SV_POSITION,
michael@0:     float4 sceneSpaceOutput : SCENE_POSITION,
michael@0:     float4 texelSpaceInput0 : TEXCOORD0
michael@0:     ) : SV_Target
michael@0: {
michael@0:   // Radial gradient painting is defined as the set of circles whose centers
michael@0:   // are described by C(t) = (C2 - C1) * t + C1; with radii
michael@0:   // R(t) = (R2 - R1) * t + R1; for R(t) > 0. This shader solves the
michael@0:   // quadratic equation that arises when calculating t for pixel (x, y).
michael@0:   //
michael@0:   // A more extensive derrivation can be found in the pixman radial gradient
michael@0:   // code.
michael@0: 
michael@0:   float2 p = float2(sceneSpaceOutput.x * transform._11 + sceneSpaceOutput.y * transform._21 + transform._31,
michael@0:                     sceneSpaceOutput.x * transform._12 + sceneSpaceOutput.y * transform._22 + transform._32);
michael@0:   float3 dp = float3(p - center1, radius1);
michael@0: 
michael@0:   // dpx * dcx + dpy * dcy + r * dr
michael@0:   float B = dot(dp, diff);
michael@0: 
michael@0:   float C = pow(dp.x, 2) + pow(dp.y, 2) - sq_radius1;
michael@0: 
michael@0:   float det = pow(B, 2) - A * C;
michael@0: 
michael@0:   float sqrt_det = sqrt(abs(det));
michael@0: 
michael@0:   float2 t = (B + float2(sqrt_det, -sqrt_det)) / A;
michael@0: 
michael@0:   float2 isValid = step(float2(-radius1, -radius1), t * diff.z);
michael@0: 
michael@0:   float upper_t = lerp(t.y, t.x, isValid.x);
michael@0: 
michael@0:   float4 output = GradientTexture.Sample(GradientSampler, float2(upper_t, 0.5));
michael@0:   // Premultiply
michael@0:   output.rgb *= output.a;
michael@0:   // Multiply the output color by the input mask for the operation.
michael@0:   output *= InputTexture.Sample(InputSampler, texelSpaceInput0.xy);
michael@0: 
michael@0:   // In order to compile for PS_4_0_level_9_3 we need to be branchless.
michael@0:   // This is essentially returning nothing, i.e. bailing early if:
michael@0:   // det < 0 || max(isValid.x, isValid.y) <= 0
michael@0:   return output * abs(step(max(isValid.x, isValid.y), 0) - 1.0f) * step(0, det);
michael@0: };
michael@0: 
michael@0: float4 SampleRadialGradientA0PS(
michael@0:     float4 clipSpaceOutput  : SV_POSITION,
michael@0:     float4 sceneSpaceOutput : SCENE_POSITION,
michael@0:     float4 texelSpaceInput0 : TEXCOORD0
michael@0:     ) : SV_Target
michael@0: {
michael@0:   // This simpler shader is used for the degenerate case where A is 0,
michael@0:   // i.e. we're actually solving a linear equation.
michael@0: 
michael@0:   float2 p = float2(sceneSpaceOutput.x * transform._11 + sceneSpaceOutput.y * transform._21 + transform._31,
michael@0:                     sceneSpaceOutput.x * transform._12 + sceneSpaceOutput.y * transform._22 + transform._32);
michael@0:   float3 dp = float3(p - center1, radius1);
michael@0: 
michael@0:   // dpx * dcx + dpy * dcy + r * dr
michael@0:   float B = dot(dp, diff);
michael@0: 
michael@0:   float C = pow(dp.x, 2) + pow(dp.y, 2) - pow(radius1, 2);
michael@0: 
michael@0:   float t = 0.5 * C / B;
michael@0: 
michael@0:   float4 output = GradientTexture.Sample(GradientSampler, float2(t, 0.5));
michael@0:   // Premultiply
michael@0:   output.rgb *= output.a;
michael@0:   // Multiply the output color by the input mask for the operation.
michael@0:   output *= InputTexture.Sample(InputSampler, texelSpaceInput0.xy);
michael@0: 
michael@0:   // In order to compile for PS_4_0_level_9_3 we need to be branchless.
michael@0:   // This is essentially returning nothing, i.e. bailing early if:
michael@0:   // -radius1 >= t * diff.z
michael@0:   return output * abs(step(t * diff.z, -radius1) - 1.0f);
michael@0: };