shaders.metal

/*
 * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

#include <simd/simd.h>
#include <metal_stdlib>
#include "common.h"

using namespace metal;

struct VertexInput {
    float2 position [[attribute(VertexAttributePosition)]];
};

struct TxtVertexInput {
    float2 position [[attribute(VertexAttributePosition)]];
    float2 texCoords [[attribute(VertexAttributeTexPos)]];
};

struct AAVertexInput {
    float2 position [[attribute(VertexAttributePosition)]];
    float2 oTexCoords [[attribute(VertexAttributeTexPos)]];
    float2 iTexCoords [[attribute(VertexAttributeITexPos)]];
};

struct ColShaderInOut {
    float4 position [[position]];
    half4  color;
};

struct AAShaderInOut {
    float4 position [[position]];
    float2 outerTexCoords;
    float2 innerTexCoords;
    half4  color;
};

struct StencilShaderInOut {
    float4 position [[position]];
    char color;
};

struct TxtShaderInOut {
    float4 position [[position]];
    float2 texCoords;
    float2 tpCoords;
};

struct LCDShaderInOut {
    float4 position [[position]];
    float2 orig_pos;
    float2 texCoords;
};

struct GradShaderInOut {
    float4 position [[position]];
    float2 texCoords;
};


struct ColShaderInOut_XOR {
    float4 position [[position]];
    float2 orig_pos;
    half4  color;
};

struct TxtShaderInOut_XOR {
    float4 position [[position]];
    float2 orig_pos;
    float2 texCoords;
    float2 tpCoords;
};

inline float fromLinear(float c)
{
    if (isnan(c)) c = 0.0;
    if (c > 1.0)
          c = 1.0;
    else if (c < 0.0)
          c = 0.0;
    else if (c < 0.0031308)
          c = 12.92 * c;
    else
    c = 1.055 * powr(c, 1.0/2.4) - 0.055;
    return c;
}

inline float3 fromLinear3(float3 c) {
    //c.r = fromLinear(c.r);
    //c.g = fromLinear(c.g);
    //c.b = fromLinear(c.b);
    // Use approximated calculations to match software rendering
    c.rgb = 1.055 * pow(c.rgb, float3(0.416667)) - 0.055;
    return c;
}

template <typename Uniforms> inline
float4 frag_single_grad(float a, Uniforms uniforms)
{
    int fa = floor(a);
    if (uniforms.isCyclic) {
        if (fa%2) {
            a = 1.0 + fa - a;
        } else {
            a = a - fa;
        }
    } else {
        a = saturate(a);
    }
    return mix(uniforms.color1, uniforms.color2, a);
}

template <typename Uniforms> inline
float4 frag_multi_grad(float a, Uniforms uniforms)
{
      if (uniforms.cycleMethod > GradNoCycle) {
          int fa = floor(a);
          a = a - fa;
          if (uniforms.cycleMethod == GradReflect && fa%2) {
              a = 1.0 - a;
          }
      } else {
          a = saturate(a);
      }

      int n = 0;
      for (;n < GRAD_MAX_FRACTIONS - 1; n++) {
          if (a <= uniforms.fract[n + 1]) break;
      }

      a = (a - uniforms.fract[n]) / (uniforms.fract[n + 1] - uniforms.fract[n]);

      float4 c = mix(uniforms.color[n], uniforms.color[n + 1], a);
      if (uniforms.isLinear) {
          c.rgb = fromLinear3(c.rgb);
      }
      return c;
}

vertex ColShaderInOut vert_col(VertexInput in [[stage_in]],
       constant FrameUniforms& uniforms [[buffer(FrameUniformBuffer)]],
       constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    ColShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.color = half4(uniforms.color.r, uniforms.color.g, uniforms.color.b, uniforms.color.a);
    return out;
}

vertex AAShaderInOut vert_col_aa(AAVertexInput in [[stage_in]],
       constant FrameUniforms& uniforms [[buffer(FrameUniformBuffer)]],
       constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    AAShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.color = half4(uniforms.color.r, uniforms.color.g, uniforms.color.b, uniforms.color.a);
    out.outerTexCoords = in.oTexCoords;
    out.innerTexCoords = in.iTexCoords;
    return out;
}

vertex StencilShaderInOut vert_stencil(VertexInput in [[stage_in]],
       constant FrameUniforms& uniforms [[buffer(FrameUniformBuffer)]],
       constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    StencilShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix * pos4;
    out.color = 0xFF;
    return out;
}

vertex GradShaderInOut vert_grad(VertexInput in [[stage_in]], constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    GradShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    return out;
}

vertex TxtShaderInOut vert_txt(TxtVertexInput in [[stage_in]], constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    TxtShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.texCoords = in.texCoords;
    return out;
}

vertex LCDShaderInOut vert_txt_lcd(TxtVertexInput in [[stage_in]], constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    LCDShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.orig_pos = in.position;
    out.texCoords = in.texCoords;
    return out;
}

vertex TxtShaderInOut vert_txt_tp(TxtVertexInput in [[stage_in]], constant AnchorData& anchorData [[buffer(FrameUniformBuffer)]], constant TransformMatrix& transform [[buffer(MatrixBuffer)]])
{
    TxtShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix * pos4;

    // Compute texture coordinates here w.r.t. anchor rect of texture paint
    out.tpCoords.x = (anchorData.xParams[0] * in.position.x) +
                      (anchorData.xParams[1] * in.position.y) +
                      (anchorData.xParams[2] * out.position.w);
    out.tpCoords.y = (anchorData.yParams[0] * in.position.x) +
                      (anchorData.yParams[1] * in.position.y) +
                      (anchorData.yParams[2] * out.position.w);
    out.texCoords = in.texCoords;

    return out;
}

vertex GradShaderInOut vert_txt_grad(TxtVertexInput in [[stage_in]],
                                     constant TransformMatrix& transform [[buffer(MatrixBuffer)]]) {
    GradShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.texCoords = in.texCoords;
    return out;
}

fragment half4 frag_col(ColShaderInOut in [[stage_in]]) {
    return in.color;
}

fragment half4 frag_col_aa(AAShaderInOut in [[stage_in]]) {
    float2 oleg1 = dfdx(in.outerTexCoords);
    float2 oleg2 = dfdy(in.outerTexCoords);
    // Calculate the bounds of the distorted pixel parallelogram.
    float2 corner = in.outerTexCoords - (oleg1+oleg2)/2.0;
    float2 omin = min(corner, corner+oleg1);
    omin = min(omin, corner+oleg2);
    omin = min(omin, corner+oleg1+oleg2);
    float2 omax = max(corner, corner+oleg1);
    omax = max(omax, corner+oleg2);
    omax = max(omax, corner+oleg1+oleg2);
    // Calculate the vectors for the "legs" of the pixel parallelogram
    // for the inner parallelogram.
    float2 ileg1 = dfdx(in.innerTexCoords);
    float2 ileg2 = dfdy(in.innerTexCoords);
    // Calculate the bounds of the distorted pixel parallelogram.
    corner = in.innerTexCoords - (ileg1+ileg2)/2.0;
    float2 imin = min(corner, corner+ileg1);
    imin = min(imin, corner+ileg2);
    imin = min(imin, corner+ileg1+ileg2);
    float2 imax = max(corner, corner+ileg1);
    imax = max(imax, corner+ileg2);
    imax = max(imax, corner+ileg1+ileg2);
    // Clamp the bounds of the parallelograms to the unit square to
    // estimate the intersection of the pixel parallelogram with
    // the unit square.  The ratio of the 2 rectangle areas is a
    // reasonable estimate of the proportion of coverage.
    float2 o1 = clamp(omin, 0.0, 1.0);
    float2 o2 = clamp(omax, 0.0, 1.0);
    float oint = (o2.y-o1.y)*(o2.x-o1.x);
    float oarea = (omax.y-omin.y)*(omax.x-omin.x);
    float2 i1 = clamp(imin, 0.0, 1.0);
    float2 i2 = clamp(imax, 0.0, 1.0);
    float iint = (i2.y-i1.y)*(i2.x-i1.x);
    float iarea = (imax.y-imin.y)*(imax.x-imin.x);
    // Proportion of pixel in outer shape minus the proportion
    // of pixel in the inner shape == the coverage of the pixel
    // in the area between the two.
    float coverage = oint/oarea - iint / iarea;
    return (in.color * coverage);
}

fragment unsigned int frag_stencil(StencilShaderInOut in [[stage_in]]) {
    return in.color;
}

// NOTE:
// 1. consider to make shaders without IF-conditions
// 2. we can pass interpolation mode via uniforms and select corresponding sampler in shader
//  but it can cause performance problems (something like getTextureSampler(hint) will be invoked
//  for every pixel)

fragment half4 frag_txt(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        constant TxtFrameUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);
    float srcA = uniforms.isSrcOpaque ? 1 : pixelColor.a;
    if (uniforms.mode) {
        float3 c = mix(pixelColor.rgb, uniforms.color.rgb, srcA);
        return half4(c.r, c.g, c.b ,
                     (uniforms.isSrcOpaque) ?
                      uniforms.color.a : pixelColor.a*uniforms.color.a);
    }

    return half4(pixelColor.r,
                 pixelColor.g,
                 pixelColor.b, srcA)*uniforms.extraAlpha;
}

fragment half4 frag_text(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        constant TxtFrameUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);
    return half4(uniforms.color * pixelColor.a);
}

fragment half4 frag_txt_tp(TxtShaderInOut vert [[stage_in]],
                       texture2d<float, access::sample> renderTexture [[texture(0)]],
                       texture2d<float, access::sample> paintTexture [[texture(1)]],
                       constant TxtFrameUniforms& uniforms [[buffer(1)]],
                       sampler textureSampler [[sampler(0)]]
) {
    float4 renderColor = renderTexture.sample(textureSampler, vert.texCoords);
    float4 paintColor = paintTexture.sample(textureSampler, vert.tpCoords);
    const float srcA = uniforms.isSrcOpaque ? 1 : paintColor.a;
    return half4(paintColor.r*renderColor.a,
                 paintColor.g*renderColor.a,
                 paintColor.b*renderColor.a,
                 srcA*renderColor.a) * uniforms.extraAlpha;
}

fragment half4 frag_txt_grad(GradShaderInOut in [[stage_in]],
                         constant GradFrameUniforms& uniforms [[buffer(0)]],
                         texture2d<float, access::sample> renderTexture [[texture(0)]])
{
    constexpr sampler textureSampler (address::repeat, mag_filter::nearest,
                                      min_filter::nearest);

    float4 renderColor = renderTexture.sample(textureSampler, in.texCoords);

    float3 v = float3(in.position.x-0.5, in.position.y-0.5, 1);
    float  a = (dot(v,uniforms.params)-0.25)*2.0;
    return half4(frag_single_grad(a, uniforms)*renderColor.a)*uniforms.extraAlpha;
}

fragment half4 frag_txt_lin_grad(GradShaderInOut in [[stage_in]],
                                 constant LinGradFrameUniforms& uniforms [[buffer(0)]],
                                 texture2d<float, access::sample> renderTexture [[texture(0)]])
{
    constexpr sampler textureSampler (address::repeat, mag_filter::nearest,
                                      min_filter::nearest);

    float4 renderColor = renderTexture.sample(textureSampler, in.texCoords);
    float3 v = float3(in.position.x, in.position.y, 1);
    float  a = dot(v,uniforms.params);
    return half4(frag_multi_grad(a, uniforms)*renderColor.a)*uniforms.extraAlpha;
}

fragment half4 frag_txt_rad_grad(GradShaderInOut in [[stage_in]],
                                 constant RadGradFrameUniforms& uniforms [[buffer(0)]],
                                 texture2d<float, access::sample> renderTexture [[texture(0)]])
{
    constexpr sampler textureSampler (address::repeat, mag_filter::nearest,
                                      min_filter::nearest);

    float4 renderColor = renderTexture.sample(textureSampler, in.texCoords);

    float3 fragCoord = float3(in.position.x-0.5, in.position.y-0.5, 1);
    float  x = dot(fragCoord, uniforms.m0);
    float  y = dot(fragCoord, uniforms.m1);
    float  xfx = x - uniforms.precalc.x;
    float  a = (uniforms.precalc.x*xfx + sqrt(xfx*xfx + y*y*uniforms.precalc.y))*uniforms.precalc.z;
    return half4(frag_multi_grad(a, uniforms)*renderColor.a)*uniforms.extraAlpha;
}


fragment half4 aa_frag_txt(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        texture2d<float, access::sample> stencilTexture [[texture(1)]],
        constant TxtFrameUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);
    if (!is_null_texture(stencilTexture)) {
        float4 stencil = stencilTexture.sample(textureSampler, vert.texCoords);
        if (stencil.r ==  0.0) {
            discard_fragment();
        }
    }
    return half4(pixelColor.r, pixelColor.g, pixelColor.b, pixelColor.a);
}

fragment half4 frag_txt_op_rescale(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> srcTex [[texture(0)]],
        constant TxtFrameOpRescaleUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 srcColor = srcTex.sample(textureSampler, vert.texCoords);
    const float srcA = uniforms.isSrcOpaque ? 1 : srcColor.a;

    // TODO: check uniforms.isNonPremult and pre-multiply if necessary
    return half4(srcColor.r*uniforms.normScaleFactors.r + uniforms.normOffsets.r,
                 srcColor.g*uniforms.normScaleFactors.g + uniforms.normOffsets.g,
                 srcColor.b*uniforms.normScaleFactors.b + uniforms.normOffsets.b, srcA)*uniforms.extraAlpha;

    // NOTE: GL-shader multiplies result with glColor (in order to apply extra alpha), probably it's better to do the
    // same here.
    //
    // GL-shader impl:
    //"    vec4 srcColor = texture%s(baseImage, gl_TexCoord[0].st);"
    //"    %s"                                                      // (placeholder for un-premult code: srcColor.rgb /= srcColor.a;)
    //"    vec4 result = (srcColor * scaleFactors) + offsets;"      // rescale source value
    //"    %s"                                                      // (placeholder for re-premult code: result.rgb *= result.a;)
    //"    gl_FragColor = result * gl_Color;"                       // modulate with gl_Color in order to apply extra alpha
}

fragment half4 frag_txt_op_convolve(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> srcTex [[texture(0)]],
        constant TxtFrameOpConvolveUniforms& uniforms [[buffer(1)]],
        const device float * kernelVals [[buffer(2)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 sum = float4(0, 0, 0, 0);
    if (vert.texCoords[0] < uniforms.imgEdge[0]
        || vert.texCoords[1] < uniforms.imgEdge[1]
        || vert.texCoords[0] > uniforms.imgEdge[2]
        || vert.texCoords[1] > uniforms.imgEdge[3]
    ) {
        if (!uniforms.isEdgeZeroFill) {
            sum = srcTex.sample(textureSampler, vert.texCoords);
        }
    }

    for (int i = 0; i < uniforms.kernelSize; i++) {
        float3 kern = float3(kernelVals[i*3], kernelVals[i*3 + 1], kernelVals[i*3 + 2]);
        float2 pos = float2(vert.texCoords.x + kern.x, vert.texCoords.y + kern.y);
        float4 pixCol = srcTex.sample(textureSampler, pos);
        sum.r += kern.z * pixCol.r;
        sum.g += kern.z * pixCol.g;
        sum.b += kern.z * pixCol.b;
        sum.a += kern.z * pixCol.a;
    }
    const float srcA = uniforms.isSrcOpaque ? 1 : sum.a;
    return half4(sum.r, sum.g, sum.b, srcA)*uniforms.extraAlpha;

    // NOTE: GL-shader multiplies result with glColor (in order to apply extra alpha), probably it's better to do the
    // same here.
    //
    // GL-shader impl:
    //"    if (any(lessThan(gl_TexCoord[0].st, imgEdge.xy)) ||"
    //"        any(greaterThan(gl_TexCoord[0].st, imgEdge.zw)))"
    //"    {"
    //"        %s"      // (placeholder for edge condition code)
    //"    } else {"
    //"        sum = vec4(0.0);"
    //"        for (i = 0; i < MAX_KERNEL_SIZE; i++) {"
    //"            sum +="
    //"                kernelVals[i].z *"
    //"                texture%s(baseImage,"
    //"                          gl_TexCoord[0].st + kernelVals[i].xy);"
    //"        }"
    //"    }"
    //""
    //"    gl_FragColor = sum * gl_Color;" // modulate with gl_Color in order to apply extra alpha
}

fragment half4 frag_txt_op_lookup(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> srcTex [[texture(0)]],
        texture2d<float, access::sample> lookupTex [[texture(1)]],
        constant TxtFrameOpLookupUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]]
) {
    float4 srcColor = srcTex.sample(textureSampler, vert.texCoords);
    float4 srcIndex = srcColor - uniforms.offset;
    const float2 posR = float2(srcIndex.r, 0.125);
    const float2 posG = float2(srcIndex.g, 0.375);
    const float2 posB = float2(srcIndex.b, 0.625);

    float4 lookupR = lookupTex.sample(textureSampler, posR);
    float4 lookupG = lookupTex.sample(textureSampler, posG);
    float4 lookupB = lookupTex.sample(textureSampler, posB);
    const float srcA = uniforms.isSrcOpaque ? 1 : srcColor.a;
    const float a = uniforms.isUseSrcAlpha ? srcA : lookupTex.sample(textureSampler, float2(srcIndex.a, 0.875)).a;

    // TODO: check uniforms.isNonPremult and pre-multiply if necessary
    return half4(lookupR.a, lookupG.a, lookupB.a, a)*uniforms.extraAlpha;

    // NOTE: GL-shader multiplies result with glColor (in order to apply extra alpha), probably it's better to do the
    // same here.
    //
    // GL-shader impl:
    //"    vec4 srcColor = texture%s(baseImage, gl_TexCoord[0].st);"
    //"    %s"                                  // (placeholder for un-premult code)
    //"    vec4 srcIndex = srcColor - offset;"  // subtract offset from original index
    //
    //      // use source value as input to lookup table (note that
    //      // "v" texcoords are hardcoded to hit texel centers of
    //      // each row/band in texture)
    //"    vec4 result;"
    //"    result.r = texture2D(lookupTable, vec2(srcIndex.r, 0.125)).r;"
    //"    result.g = texture2D(lookupTable, vec2(srcIndex.g, 0.375)).r;"
    //"    result.b = texture2D(lookupTable, vec2(srcIndex.b, 0.625)).r;"
    //"    %s"                                  // (placeholder for alpha store code)
    //"    %s"                                  // (placeholder for re-premult code)
    //"    gl_FragColor = result * gl_Color;"   // modulate with gl_Color in order to apply extra alpha
}

fragment half4 frag_grad(GradShaderInOut in [[stage_in]],
                         constant GradFrameUniforms& uniforms [[buffer(0)]]) {
    float3 v = float3(in.position.x-0.5, in.position.y-0.5, 1);
    float  a = (dot(v,uniforms.params)-0.25)*2.0;
    return half4(frag_single_grad(a, uniforms)) * uniforms.extraAlpha;
}

// LinGradFrameUniforms
fragment half4 frag_lin_grad(GradShaderInOut in [[stage_in]],
                             constant LinGradFrameUniforms& uniforms [[buffer(0)]]) {
    float3 v = float3(in.position.x-0.5, in.position.y-0.5, 1);
    float  a = dot(v, uniforms.params);
    return half4(frag_multi_grad(a, uniforms))*uniforms.extraAlpha;
}

fragment half4 frag_rad_grad(GradShaderInOut in [[stage_in]],
                             constant RadGradFrameUniforms& uniforms [[buffer(0)]]) {
    float3 fragCoord = float3(in.position.x-0.5, in.position.y-0.5, 1);
    float  x = dot(fragCoord, uniforms.m0);
    float  y = dot(fragCoord, uniforms.m1);
    float  xfx = x - uniforms.precalc.x;
    float  a = (uniforms.precalc.x*xfx + sqrt(xfx*xfx + y*y*uniforms.precalc.y))*uniforms.precalc.z;
    return half4(frag_multi_grad(a, uniforms))*uniforms.extraAlpha;
}

vertex TxtShaderInOut vert_tp(VertexInput in [[stage_in]],
       constant AnchorData& anchorData [[buffer(FrameUniformBuffer)]],
       constant TransformMatrix& transform [[buffer(MatrixBuffer)]])
{
    TxtShaderInOut out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix * pos4;

    // Compute texture coordinates here w.r.t. anchor rect of texture paint
    out.texCoords.x = (anchorData.xParams[0] * in.position.x) +
                      (anchorData.xParams[1] * in.position.y) +
                      (anchorData.xParams[2] * out.position.w);
    out.texCoords.y = (anchorData.yParams[0] * in.position.x) +
                      (anchorData.yParams[1] * in.position.y) +
                      (anchorData.yParams[2] * out.position.w);

    return out;
}

fragment half4 frag_tp(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        constant TxtFrameUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]])
{
    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);
    const float srcA = uniforms.isSrcOpaque ? 1 : pixelColor.a;
    return half4(pixelColor.r, pixelColor.g, pixelColor.b, srcA) * uniforms.extraAlpha;
}



/* The variables involved in the equation can be expressed as follows:
 *
 *   Cs = Color component of the source (foreground color) [0.0, 1.0]
 *   Cd = Color component of the destination (background color) [0.0, 1.0]
 *   Cr = Color component to be written to the destination [0.0, 1.0]
 *   Ag = Glyph alpha (aka intensity or coverage) [0.0, 1.0]
 *   Ga = Gamma adjustment in the range [1.0, 2.5]
 *   (^ means raised to the power)
 *
 * And here is the theoretical equation approximated by this shader:
 *
 *            Cr = (Ag*(Cs^Ga) + (1-Ag)*(Cd^Ga)) ^ (1/Ga)
 */
fragment float4 lcd_color(
        LCDShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> glyphTexture [[texture(0)]],
        texture2d<float, access::sample> dstTexture [[texture(1)]],
        constant LCDFrameUniforms& uniforms [[buffer(1)]])
{
    float3 src_adj = uniforms.src_adj;
    float3 gamma = uniforms.gamma;
    float3 invgamma = uniforms.invgamma;

    constexpr sampler glyphTextureSampler (address::repeat,
                                      mag_filter::nearest,
                                      min_filter::nearest);

    // load the RGB value from the glyph image at the current texcoord
    float3 glyph_clr = float3(glyphTexture.sample(glyphTextureSampler, vert.texCoords));

    if (glyph_clr.r == 0.0f && glyph_clr.g == 0.0f && glyph_clr.b == 0.0f) {
        // zero coverage, so skip this fragment
        discard_fragment();
    }

    // load the RGB value from the corresponding destination pixel
    uint2 texCoord = {(unsigned int)(vert.orig_pos.x), (unsigned int)(vert.orig_pos.y)};
    float4 dst_clr = dstTexture.read(texCoord);

    // gamma adjust the dest color
    float3 dst_adj = pow(dst_clr.rgb, gamma);

    // linearly interpolate the three color values
    float3 result = mix(dst_adj, src_adj, glyph_clr);

    // gamma re-adjust the resulting color (alpha is always set to 1.0)
    return float4(pow(result.rgb, invgamma), 1.0);

}
// Compute shader to transfer clipping data to the texture used for manual clipping in
// aa_frag_txt shader
kernel void stencil2tex(const device uchar *imageBuffer [[buffer(0)]],
    device uchar4 *outputBuffer [[buffer(1)]],
    uint gid [[thread_position_in_grid]])
{
    uchar p = imageBuffer[gid];
    outputBuffer[gid] = uchar4(p, p, p, p);
}

// work item deals with 4 byte pixel
// assuming that data is aligned
kernel void rgb_to_rgba(const device uchar *imageBuffer [[buffer(0)]],
                        device uchar *outputBuffer [[buffer(1)]],
                        uint gid [[thread_position_in_grid]])
{
    outputBuffer[4 * gid]     = imageBuffer[4 * gid];     // r
    outputBuffer[4 * gid + 1] = imageBuffer[4 * gid + 1]; // g
    outputBuffer[4 * gid + 2] = imageBuffer[4 * gid + 2]; // b
    outputBuffer[4 * gid + 3] = 255;                      // a
}

kernel void bgr_to_rgba(const device uchar *imageBuffer [[buffer(0)]],
                        device uchar *outputBuffer [[buffer(1)]],
                        uint gid [[thread_position_in_grid]])
{
    outputBuffer[4 * gid]     = imageBuffer[4 * gid + 2]; // r
    outputBuffer[4 * gid + 1] = imageBuffer[4 * gid + 1]; // g
    outputBuffer[4 * gid + 2] = imageBuffer[4 * gid];     // b
    outputBuffer[4 * gid + 3] = 255;                      // a
}

kernel void xrgb_to_rgba(const device uchar *imageBuffer [[buffer(0)]],
                         device uchar *outputBuffer [[buffer(1)]],
                         uint gid [[thread_position_in_grid]])
{
    outputBuffer[4 * gid]     = imageBuffer[4 * gid + 1]; // r
    outputBuffer[4 * gid + 1] = imageBuffer[4 * gid + 2]; // g
    outputBuffer[4 * gid + 2] = imageBuffer[4 * gid + 3]; // b
    outputBuffer[4 * gid + 3] = imageBuffer[4 * gid];     // a
}


kernel void xbgr_to_rgba(const device uchar *imageBuffer [[buffer(0)]],
                         device uchar *outputBuffer [[buffer(1)]],
                         uint gid [[thread_position_in_grid]])
{
    outputBuffer[4 * gid]     = imageBuffer[4 * gid + 3]; // r
    outputBuffer[4 * gid + 1] = imageBuffer[4 * gid + 2]; // g
    outputBuffer[4 * gid + 2] = imageBuffer[4 * gid + 1]; // b
    outputBuffer[4 * gid + 3] = imageBuffer[4 * gid];     // a
}

// ----------------------------------------------------------------------------
// Shaders for rendering in XOR Mode
// ----------------------------------------------------------------------------
vertex ColShaderInOut_XOR vert_col_xorMode(VertexInput in [[stage_in]],
       constant FrameUniforms& uniforms [[buffer(FrameUniformBuffer)]],
       constant TransformMatrix& transform [[buffer(MatrixBuffer)]])
{
    ColShaderInOut_XOR out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.orig_pos = in.position;
    out.color = half4(uniforms.color.r, uniforms.color.g, uniforms.color.b, uniforms.color.a);
    return out;
}

fragment half4 frag_col_xorMode(ColShaderInOut_XOR in [[stage_in]],
        texture2d<float, access::read> renderTexture [[texture(0)]])
{
    uint2 texCoord = {(unsigned int)(in.orig_pos.x), (unsigned int)(in.orig_pos.y)};

    float4 pixelColor = renderTexture.read(texCoord);
    half4 color = in.color;

    half4 c;
    c.r = float( (unsigned char)(pixelColor.r * 255.0) ^ (unsigned char)(color.r * 255.0)) / 255.0f;
    c.g = float( (unsigned char)(pixelColor.g * 255.0) ^ (unsigned char)(color.g * 255.0)) / 255.0f;
    c.b = float( (unsigned char)(pixelColor.b * 255.0) ^ (unsigned char)(color.b * 255.0)) / 255.0f;
    c.a = 1.0;

    return c;
}


vertex TxtShaderInOut_XOR vert_txt_xorMode(
        TxtVertexInput in [[stage_in]],
        constant TransformMatrix& transform [[buffer(MatrixBuffer)]])
{
    TxtShaderInOut_XOR out;
    float4 pos4 = float4(in.position, 0.0, 1.0);
    out.position = transform.transformMatrix*pos4;
    out.orig_pos = in.position;
    out.texCoords = in.texCoords;
    return out;
}

fragment half4 frag_txt_xorMode(
        TxtShaderInOut_XOR vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        texture2d<float, access::read> backgroundTexture [[texture(1)]],
        constant TxtFrameUniforms& uniforms [[buffer(1)]],
        sampler textureSampler [[sampler(0)]])
{
    uint2 texCoord = {(unsigned int)(vert.orig_pos.x), (unsigned int)(vert.orig_pos.y)};
    float4 bgColor = backgroundTexture.read(texCoord);

    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);
    float srcA = uniforms.isSrcOpaque ? 1 : pixelColor.a;

    float4 c;
    if (uniforms.mode) {
        c = mix(pixelColor, uniforms.color, srcA);
    } else {
        c = float4(pixelColor.r,
                 pixelColor.g,
                 pixelColor.b, srcA)*uniforms.extraAlpha;
    }

    half4 ret;
    ret.r = half( (unsigned char)(c.r * 255.0) ^ (unsigned char)(bgColor.r * 255.0)) / 255.0f;
    ret.g = half( (unsigned char)(c.g * 255.0) ^ (unsigned char)(bgColor.g * 255.0)) / 255.0f;
    ret.b = half( (unsigned char)(c.b * 255.0) ^ (unsigned char)(bgColor.b * 255.0)) / 255.0f;
    ret.a = c.a + (1.0 - c.a) * bgColor.a;

    return ret;
}


/*
    // --------------------------------------------------------------------------------------
    Currently, gradient paint and texture paint XOR mode rendering has been implemented
    through tile based rendering (similar to OGL) that uses MTLBlitLoops_SurfaceToSwBlit method for
    getting framebuffer tiles and render using a different render pipe (not MTLRenderer)

    In metal, we can avoid tile based rendering and use below shaders.
    NOTE: These two shaders are incomplete and need some tweak.
    // --------------------------------------------------------------------------------------

fragment half4 frag_grad_xorMode(GradShaderInOut_XOR in [[stage_in]],
                         texture2d<float, access::read> renderTexture [[texture(0)]],
                         constant GradFrameUniforms& uniforms [[buffer(0)]]) {
    uint2 texCoord = {(unsigned int)(in.orig_pos.x), (unsigned int)(in.orig_pos.y)};
    float4 pixelColor = renderTexture.read(texCoord);

    float3 v = float3(in.position.x, in.position.y, 1);
    float  a = (dot(v,uniforms.params)-0.25)*2.0;
    float4 c = mix(uniforms.color1, uniforms.color2, a);

    half4 ret;
    ret.r = float( (unsigned char)(pixelColor.r * 255.0) ^ (unsigned char)(c.r * 255.0)) / 255.0f;
    ret.g = float( (unsigned char)(pixelColor.g * 255.0) ^ (unsigned char)(c.g * 255.0)) / 255.0f;
    ret.b = float( (unsigned char)(pixelColor.b * 255.0) ^ (unsigned char)(c.b * 255.0)) / 255.0f;

    return half4(ret);
}


fragment half4 frag_tp_xorMode(
        TxtShaderInOut vert [[stage_in]],
        texture2d<float, access::sample> renderTexture [[texture(0)]],
        texture2d<float, access::read> backgroundTexture [[texture(1)]],
        constant int& xorColor[[buffer(0)]])
{
    uint2 texCoord = {(unsigned int)(vert.orig_pos.x), (unsigned int)(vert.orig_pos.y)};
    float4 bgColor = backgroundTexture.read(texCoord);

    constexpr sampler textureSampler (address::repeat,
                                      mag_filter::nearest,
                                      min_filter::nearest);

    float4 pixelColor = renderTexture.sample(textureSampler, vert.texCoords);

    pixelColor.r = float( (unsigned char)(pixelColor.r * 255.0) ^ ((xorColor >> 16) & 0xFF) ) / 255.0f;
    pixelColor.g = float( (unsigned char)(pixelColor.g * 255.0) ^ ((xorColor >> 8) & 0xFF)) / 255.0f;
    pixelColor.b = float( (unsigned char)(pixelColor.b * 255.0) ^ (xorColor & 0xFF)) / 255.0f;
    pixelColor.a = 1.0;

    half4 ret;
    ret.r = half( (unsigned char)(pixelColor.r * 255.0) ^ (unsigned char)(bgColor.r * 255.0)) / 255.0f;
    ret.g = half( (unsigned char)(pixelColor.g * 255.0) ^ (unsigned char)(bgColor.g * 255.0)) / 255.0f;
    ret.b = half( (unsigned char)(pixelColor.b * 255.0) ^ (unsigned char)(bgColor.b * 255.0)) / 255.0f;
    ret.a = 1.0;

    return ret;

    // This implementation defaults alpha to 1.0 as if source is opaque
    //TODO : implement alpha component value if source is transparent
}
*/