% File: hawkdraw-opacity.code.tex
% Copyright 2026 Jasper Habicht (mail(at)jasperhabicht.de).
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License version 1.3c,
% available at http://www.latex-project.org/lppl/.
%
% This file is part of the `hawkdraw' package (The Work in LPPL)
% and all files in that bundle must be distributed together.
%
% This work has the LPPL maintenance status `maintained'.
%
% BOF

% v0.4.1 2026-07-08

% =====

% Opacity groups

% ===

% For opacity groups, the relevant scope is grabbed and stored in an XObject, setting the opacity inside
% the XObject to 1 (fully opaque). The XObject is then placed in a box which is then replaced into the
% drawing in a scope with the intended opacity selected and adhering to the bounding box of the original
% scope (of which the lower left corner are stored when the XObject is created).

% ===

\dim_new:N \g_hawkdraw_opacity_group_bbox_xmin_dim
\dim_new:N \g_hawkdraw_opacity_group_bbox_ymin_dim

\int_new:N \g__hawkdraw_opacity_group_int
\box_new:N \l__hawkdraw_opacity_group_box

\cs_new_protected:Npn \hawkdraw_opacity_group_set_use:n #1 {
    \pdfxform_new:nnn {
        hawkdraw_opacity_group_ \int_use:N \g__hawkdraw_opacity_group_int
    } {
        /Group ~ << ~
            /S ~ /Transparency ~
            /I ~ true ~
            /K ~ false ~
        >>
    } {
        \draw_suspend_begin:
            \draw_begin:
                \fp_if_nan:nF { \l_hawkdraw_picture_baseline_fp } {
                    \draw_set_baseline:n { -1 * \l_hawkdraw_picture_baseline_fp }
                }
                \fp_set:Nn \l_hawkdraw_path_opacity_stroke_fp { 1.0 }
                \fp_set:Nn \l_hawkdraw_path_opacity_fill_fp { 1.0 }
                #1
            \draw_end:
            \dim_gset_eq:NN
                \g_hawkdraw_opacity_group_bbox_xmin_dim
                \g_draw_bb_xmin_dim
            \dim_gset_eq:NN
                \g_hawkdraw_opacity_group_bbox_ymin_dim
                \g_draw_bb_ymin_dim
        \draw_suspend_end:
    }
    \hbox_set:Nn \l__hawkdraw_opacity_group_box {
        \pdfxform_use:n {
            hawkdraw_opacity_group_ \int_use:N \g__hawkdraw_opacity_group_int
        }
    }
    \opacity_stroke:V \l_hawkdraw_path_opacity_stroke_fp
    \opacity_fill:V \l_hawkdraw_path_opacity_fill_fp
    \draw_box_use:Nn \l__hawkdraw_opacity_group_box {
        \g_hawkdraw_opacity_group_bbox_xmin_dim
    ,
        \g_hawkdraw_opacity_group_bbox_ymin_dim
    }
}

\keys_define:nn { hawkdraw / scope } {
    opacity ~ group         .code:n         = {
        \int_gincr:N \g__hawkdraw_opacity_group_int
        \cs_set_protected:Npn \hawkdraw_scope_use:n ##1 {
            \hawkdraw_opacity_group_set_use:n {##1}
        }
    } ,
}

% =====

% Soft masks

% ===

% Soft masks need to be defined and added to the page resources before they are used. Therefore, we
% first store the path that should become the soft mask in a box. Since we want the full functionality
% of the hawkdraw environment, we use a separate environment to define the soft mask.

% When the soft mask is used, this box is placed in an XObject. Then, another XObject is created that
% has the size of the first box and refers to the XObject containing the soft mask. This XObject is set
% to be a transparency group with grayscale color space.

% This XObject is then used as reference in the page resources. The soft mask is activated by placing
% the reference into the drawing setting the graphic state shifted by the offset of the lower left
% corner of the soft mask bounding box from the origin which was stored upon creating the first box.

% ===

\msg_new:nnn { hawkdraw } { softmask-defined } {
    Soft ~ mask ~ `#1` ~ already ~ defined.
}

\msg_new:nnn { hawkdraw } { softmask-undefined } {
    Soft ~ mask ~ `#1` ~ undefined.
}

\box_new:N \l__hawkdraw_softmask_ref_box

\cs_generate_variant:Nn \draw_box_use:Nn { c }

\cs_new_protected:Npn \hawkdraw_softmask_set:nn #1#2 {
    \box_if_exist:cTF {
        g_hawkdraw_softmask_ #1 _box
    } {
        \msg_warning:nnn { hawkdraw } { softmask-defined } {#1}
    } {
        \box_new:c { g_hawkdraw_softmask_ #1 _box }
        \dim_new:c { g_hawkdraw_softmask_ #1 _bbox_xmin_dim }
        \dim_new:c { g_hawkdraw_softmask_ #1 _bbox_ymin_dim }
        \group_begin:
            \dim_set:Nn \tex_parindent:D { 0pt }
            \hbox_gset:cn { g_hawkdraw_softmask_ #1 _box } {
                \vbox:n {#2}
            }
        \group_end:
        \dim_gset_eq:cN { g_hawkdraw_softmask_ #1 _bbox_xmin_dim } {
            \g_draw_bb_xmin_dim
        }
        \dim_gset_eq:cN { g_hawkdraw_softmask_ #1 _bbox_ymin_dim } {
            \g_draw_bb_ymin_dim
        }
    }
}

\cs_new_protected:Npn \hawkdraw_softmask_use:nn #1#2 {
    \box_if_exist:cTF {
        g_hawkdraw_softmask_ #1 _box
    } {
        \pdfxform_new:nnn { hawkdraw_softmask_ #1 } { } {
            \box_use:c { g_hawkdraw_softmask_ #1 _box }
        }
        \int_const:cn {
            c__hawkdraw_softmask_ #1 _int
        } {
            \hawkdraw_support_pdflastxform:
        }

        \hbox_set_to_wd:Nnn \l__hawkdraw_softmask_ref_box {
            \box_wd:c { g_hawkdraw_softmask_ #1 _box }
        } {
            \vbox_to_ht:nn {
                \box_ht_plus_dp:c { g_hawkdraw_softmask_ #1 _box }
            } {
                \skip_vertical:n { 0pt plus 1fil }
                \hawkdraw_support_pdfliteral:n {
                    /Fm \int_use:c { c__hawkdraw_softmask_ #1 _int } ~ Do
                }
            }
            \skip_horizontal:n { 0pt plus 1fil }
        }
        \hawkdraw_support_pdfxform:nnN {
            /Group ~ << ~
                /S ~ /Transparency ~
                /CS ~ /DeviceGray ~
            >>
        } {
            /XObject ~ << ~
                /Fm \int_use:c { c__hawkdraw_softmask_ #1 _int } ~
                    \pdfxform_ref:n { hawkdraw_softmask_ #1 } ~
            >>
        } \l__hawkdraw_softmask_ref_box
        \int_const:cn {
            c__hawkdraw_softmask_object_ #1 _int
        } {
            \hawkdraw_support_pdflastxform:
        }

        \pdfmanagement_add:nee {
            Page / Resources / ExtGState
        } {
            hawkdraw Softmask
            \int_use:c {
                c__hawkdraw_softmask_object_ #1 _int
            }
        } {
            << ~
                /SMask ~ << ~
                    /S ~ /Luminosity ~
                    /G ~ \int_use:c { c__hawkdraw_softmask_object_ #1 _int } ~ 0 ~ R ~
                >> ~
            >>
        }

        \hawkdraw_support_pdfliteral:n {
            1 ~ 0 ~ 0 ~ 1 ~
            \dim_to_decimal_in_bp:n {
                \use:c { g_hawkdraw_softmask_ #1 _bbox_xmin_dim }
            } ~
            \dim_to_decimal_in_bp:n {
                \use:c { g_hawkdraw_softmask_ #1 _bbox_ymin_dim }
            } ~ cm
        }
        \hawkdraw_support_pdfliteral:n {
            /hawkdraw Softmask
            \int_use:c {
                c__hawkdraw_softmask_object_ #1 _int
            }
            \c_space_tl gs
        }
        \hawkdraw_support_pdfliteral:n {
            1 ~ 0 ~ 0 ~ 1 ~
            \dim_to_decimal_in_bp:n {
                - \use:c { g_hawkdraw_softmask_ #1 _bbox_xmin_dim }
            } ~
            \dim_to_decimal_in_bp:n {
                - \use:c { g_hawkdraw_softmask_ #1 _bbox_ymin_dim }
            } ~ cm
        }
        #2
    } {
        \msg_warning:nnn { hawkdraw } { softmask-undefined } {#1}
    }
}

\NewDocumentEnvironment { hawkdrawsoftmask } { m O{} +b } { } {
    \__hawkdraw_error_unsupported:n { Soft ~ mask }
    \hawkdraw_softmask_set:nn {#1} {
        \begin{hawkdraw}[#2]
            #3
        \end{hawkdraw}
    }
}

\keys_define:nn { hawkdraw / scope } {
    soft ~ mask ~ use       .code:n         = {
        \cs_set_protected:Npn \hawkdraw_scope_use:n ##1 {
            \hawkdraw_softmask_use:nn {#1} {##1}
        }
    } ,
}

% =====

% Blend modes

% ===

% Blend modes are activated and deactivated using a stack. We define a new color stack for this purpose.
% The stack is initialized with the default blend mode (Normal). When a blend mode is set, it is pushed
% onto the stack and the corresponding ExtGState resource is added to the relevant page. When the scope
% ends, the blend mode is popped from the stack and the Normal blend mode is restored.

% ===

\msg_new:nnn { hawkdraw } { blendmode-unknown } {
    Blend ~ mode ~ `#1` ~ unknown.
}

\prop_const_from_keyval:Nn \c__hawkdraw_blendmode_prop {
    normal        = Normal ,
    multiply      = Multiply ,
    screen        = Screen ,
    overlay       = Overlay ,
    darken        = Darken ,
    lighten       = Lighten ,
    color ~ dodge = ColorDodge ,
    color ~ burn  = ColorBurn ,
    hard ~ light  = HardLight ,
    soft ~ light  = SoftLight ,
    difference    = Difference ,
    exclusion     = Exclusion ,
    saturation    = Saturation ,
    color         = Color ,
    hue           = Hue ,
    luminosity    = Luminosity ,
}

\clist_new:N \c__hawkdraw_blendmode_active_clist

\cs_new_protected:Npn \hawkdraw_blendmode_stack_push:n #1 {
    \hawkdraw_support_pdfcolorstack:e {
        \int_use:N \c__hawkdraw_blendmode_stack_int ~ push ~ {
            /hawkdraw Blendmode \prop_item:Nn \c__hawkdraw_blendmode_prop {#1} ~ gs
        }
    }
}

\cs_new_protected:Npn \hawkdraw_blendmode_stack_pop: {
    \hawkdraw_support_pdfcolorstack:e {
        \int_use:N \c__hawkdraw_blendmode_stack_int ~ pop \scan_stop:
    }
}

\cs_new_protected:Npn \hawkdraw_blendmode_set:nn #1#2 {
    \int_if_exist:NF \c__hawkdraw_blendmode_stack_int {
        \int_const:Nn \c__hawkdraw_blendmode_stack_int {
            \hawkdraw_support_pdfcolorstackinit:n {
                page ~ direct ~ {
                    /hawkdraw Blendmode Normal ~ gs
                }
            }
        }
    }
    \prop_if_in:NnTF \c__hawkdraw_blendmode_prop {#1} {
        \clist_if_in:NnF \c__hawkdraw_blendmode_active_clist { normal } {
            \pdfmanagement_add:nnn {
                Page / Resources / ExtGState
            } {
                hawkdraw Blendmode Normal
            } {
                << ~ /BM ~ /Normal ~ >>
            }
            \clist_put_right:Nn \c__hawkdraw_blendmode_active_clist { normal }
        }
        \clist_if_in:NnF \c__hawkdraw_blendmode_active_clist {#1} {
            \pdfmanagement_add:nee {
                Page / Resources / ExtGState
            } {
                hawkdraw Blendmode \prop_item:Nn \c__hawkdraw_blendmode_prop {#1}
            } {
                << ~ /BM ~ / \prop_item:Nn \c__hawkdraw_blendmode_prop {#1} ~ >>
            }
            \clist_put_right:Nn \c__hawkdraw_blendmode_active_clist {#1}
        }
        \hawkdraw_blendmode_stack_push:n {#1}
        #2
        \hawkdraw_blendmode_stack_pop:
    } {
        \msg_warning:nnn { hawkdraw } { blendmode-unknown } {#1}
    }
}

\keys_define:nn { hawkdraw / scope } {
    blend ~ mode            .code:n         = {
        \__hawkdraw_error_unsupported:n { Blend ~ mode }
        \cs_set_protected:Npn \hawkdraw_scope_use:n ##1 {
            \hawkdraw_blendmode_set:nn {#1} {##1}
        }
    } ,
}

% EOF