implement blend mode selection in shader and fix alpha lock

data/layout.xml

@@ -158,7 +158,7 @@
           </node>
           <border dir="col" align="center" grow="1" width="1" flood-events="1">
             <node height="30" pad="1" width="100%" dir="row">
-              <combobox id="btn-ok" text="Normal" width="100%" height="30"/>
+              <combobox id="blend-mode" text="Normal" width="100%" height="30"/>
             </node>
             <node height="20" pad="1" width="100%" dir="row">
               <slider-h id="tip-size"  width="1" grow="1" value=".25"/>

engine/app_shaders.cpp

@@ -84,6 +84,7 @@ void App::initShaders()
         "uniform sampler2D tex_stencil;\n"
         //"uniform image2D   img_mixer;\n"
         "uniform mediump float alpha;\n"
+        "uniform mediump int blend_mode;\n"
         "uniform bool lock;\n"
         "uniform bool mask;\n"
         "in mediump vec3 uv;\n"
@@ -100,10 +101,16 @@ void App::initShaders()
         "   sum += textureOffset(t, uv, ivec2( 1,  1));\n"
         "   return sum / vec4(9.0);\n"
         "}\n"
-        "vec3 blend_colorDodge(vec4 base, vec4 stroke, float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, base.rgb/(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+        "vec3 blend_normal(vec4 base, vec4 stroke, float alpha_tot) { return mix(base.rgb, stroke.rgb, stroke.a/alpha_tot); }\n"
         "vec3 blend_multiply(vec4 base, vec4 stroke, float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, base.rgb*stroke.rgb, stroke.a/alpha_tot), base.a/alpha_tot); }\n"
         "vec3 blend_screen(vec4 base, vec4 stroke, float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, 1.0-(1.0-base.rgb)*(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
-        "vec3 blend_normal(vec4 base, vec4 stroke, float alpha_tot) { return mix(base.rgb, stroke.rgb, stroke.a/alpha_tot); }\n"
+        "vec3 blend_colorDodge(vec4 base, vec4 stroke, float alpha_tot) { return mix(stroke.rgb, mix(base.rgb, base.rgb/(1.0-stroke.rgb), stroke.a/alpha_tot), base.a/alpha_tot); }\n"
+        "vec3 blend(vec4 base, vec4 stroke, float alpha_tot, int mode) { switch(mode){\n"
+        "   case 0: return blend_normal(base, stroke, alpha_tot);"
+        "   case 1: return blend_multiply(base, stroke, alpha_tot);"
+        "   case 2: return blend_screen(base, stroke, alpha_tot);"
+        "   case 3: return blend_colorDodge(base, stroke, alpha_tot);"
+        "}}\n"
         "void main(){\n"
         "   mediump vec2 uv2 = gl_FragCoord.st / vec2(2048) * 20.0;\n"
         "   mediump vec4 base = texture(tex, uv.xy);\n"
@@ -111,10 +118,10 @@ void App::initShaders()
         "   mediump float stencil = pow(texture(tex_stencil, uv2).r, 8.0);\n"
         "   stroke.a = mask ? stroke.a * alpha * blur(tex_mask, uv.xy).r : stroke.a * alpha;\n"
 
-        "   if (base.a == 0.0) { frag = stroke; return; }\n"
+        "   if (!lock && base.a == 0.0) { frag = stroke; return; }\n"
         "   mediump float contribution = (1.0 - base.a) * stroke.a;\n"
         "   mediump float alpha_tot = base.a + contribution;"
-        "   mediump vec3 rgb = blend_screen(base, stroke, alpha_tot);\n"
+        "   mediump vec3 rgb = blend(base, stroke, alpha_tot, blend_mode);\n"
         "   frag = vec4(rgb, (lock ? base.a : alpha_tot));\n"
         "}\n";
 

engine/brush.h

@@ -25,6 +25,7 @@ public:
     float m_jitter_angle = 0;
     float m_jitter_spread = 0;
     float m_jitter_flow = 0;
+    int m_blend_mode = 0;
 };
 
 struct StrokeSample

engine/canvas.cpp

@@ -506,7 +506,8 @@ void ui::Canvas::stroke_commit()
             ui::ShaderManager::u_int(kShaderUniform::TexMask, 2);
             ui::ShaderManager::u_float(kShaderUniform::Alpha, m_current_stroke->m_brush.m_tip_opacity);
             ui::ShaderManager::u_int(kShaderUniform::Mask, m_smask_active);
-            ShaderManager::u_mat4(kShaderUniform::MVP, glm::ortho(-.5f, .5f, -.5f, .5f, -1.f, 1.f));
+            ui::ShaderManager::u_int(kShaderUniform::BlendMode, m_current_stroke->m_brush.m_blend_mode);
+            ui::ShaderManager::u_mat4(kShaderUniform::MVP, glm::ortho(-.5f, .5f, -.5f, .5f, -1.f, 1.f));
 
             glActiveTexture(GL_TEXTURE0);
             m_tex2[i].bind();

engine/node_canvas.cpp

@@ -153,6 +153,7 @@ void NodeCanvas::draw()
                 ui::ShaderManager::u_float(kShaderUniform::Alpha, m_canvas->m_current_stroke->m_brush.m_tip_opacity);
                 ui::ShaderManager::u_int(kShaderUniform::Lock, m_canvas->m_layers[m_canvas->m_current_layer_idx].m_alpha_locked);
                 ui::ShaderManager::u_int(kShaderUniform::Mask, m_canvas->m_smask_active);
+                ui::ShaderManager::u_int(kShaderUniform::BlendMode, m_canvas->m_current_stroke->m_brush.m_blend_mode);
                 ui::ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp_z);
                 glActiveTexture(GL_TEXTURE0);
                 m_canvas->m_layers[layer_index].m_rtt[plane_index].bindTexture();

engine/node_combobox.cpp

@@ -28,12 +28,14 @@ void NodeComboBox::loaded()
             btn->m_text->set_text(labels[i].c_str());
             btn->m_border->SetWidthP(100.f);
             btn->m_border->SetHeight(30.f);
-            btn->on_click = [this,popup](Node* target) {
+            btn->on_click = [this,popup,btn](Node* target) {
                 int index = popup->get_child_index(target);
                 m_current_index = index;
                 m_text->set_text(labels[index].c_str());
                 popup->mouse_release();
                 popup->destroy();
+                if (on_select)
+                    on_select(btn, index);
             };
         }
         glm::vec2 pos = m_pos + glm::vec2(0, m_size.y - (m_current_index+1) * 30.f);

engine/node_combobox.h

@@ -4,6 +4,7 @@
 class NodeComboBox : public NodeButton
 {
 public:
+    std::function<void(Node* target, int index)> on_select;
     std::array<std::string, 4> labels{ "Normal", "Multiply", "Screen", "Color Dodge" };
     int m_current_index = 0;
     virtual Node* clone_instantiate() const override;

engine/node_panel_stroke.cpp

@@ -43,6 +43,10 @@ void NodePanelStroke::update_controls()
 void NodePanelStroke::init_controls()
 {
     m_preview = find<NodeStrokePreview>("canvas");
+    m_blend_mode = find<NodeComboBox>("blend-mode");
+    m_blend_mode->on_select = [](Node*, int index) {
+        ui::Canvas::I->m_current_brush.m_blend_mode = index;
+    };
 
     init_slider(m_tip_size, "tip-size", &ui::Brush::m_tip_size);
     init_slider(m_tip_spacing, "tip-spacing", &ui::Brush::m_tip_spacing);

engine/node_panel_stroke.h

@@ -4,11 +4,13 @@
 #include "node_slider.h"
 #include "brush.h"
 #include "node_checkbox.h"
+#include "node_combobox.h"
 
 class NodePanelStroke : public Node
 {
 public:
     NodeStrokePreview* m_preview;
+    NodeComboBox* m_blend_mode;
     NodeSliderH* m_tip_size;
     NodeSliderH* m_tip_spacing;
     NodeSliderH* m_tip_flow;

engine/shader.h

@@ -23,6 +23,7 @@ enum class kShaderUniform : uint16_t
     Mask  = const_hash("mask"),
     Resolution = const_hash("resolution"),
     Highlight = const_hash("highlight"),
+    BlendMode = const_hash("blend_mode"),
 };
 
 enum class kShader : uint16_t