added orthogonal slicing to volume renderer and to corresponding example

libs/cgv_gl/glsl/volume.glfs

@@ -43,6 +43,11 @@ mat3 get_inverse_normal_matrix();
 #define ISOSURFACE_MODE 0
 #define ISOSURFACE_COLOR_MODE 0
 
+// 0 - Disabled
+// 1 - Opaque
+// 2 - Transparent
+#define SLICE_MODE 0
+
 // automatic defines
 #define TRANSFER_FUNCTION_SAMPLER_DIMENSIONS 1
 
@@ -77,12 +82,12 @@ layout (binding = 3) uniform sampler3D gradient_tex;
 layout (binding = 4) uniform sampler2D depth_tex;
 #endif
 
-uniform vec2 viewport_dims;
-uniform vec2 noise_offset;
+uniform vec2  viewport_dims;
+uniform vec2  noise_offset;
 uniform float scale_adjustment_factor;
 
-uniform bool light_local_to_eye;
-uniform vec3 light_direction;
+uniform bool  light_local_to_eye;
+uniform vec3  light_direction;
 uniform float ambient_strength;
 uniform float diffuse_strength;
 uniform float specular_strength;
@@ -92,10 +97,14 @@ uniform float specular_color_mix;
 uniform float gradient_lambda;
 
 uniform float isovalue;
-uniform vec3 isosurface_color;
+uniform vec3  isosurface_color;
+
+uniform int   slice_axis;
+uniform float slice_coordinate;
+uniform float slice_opacity;
 
-uniform vec3 clip_box_min;
-uniform vec3 clip_box_max;
+uniform vec3  clip_box_min;
+uniform vec3  clip_box_max;
 
 // in/out parameters
 in vec3 position_object;
@@ -382,6 +391,9 @@ void main() {
 	// initial color with full transparency for front-to-back blending
 	vec4 color = vec4(0.0, 0.0, 0.0, 1.0);
 	// step count (needed later for averaging the density if using average compositing mode)
+#if SLICE_MODE > 0
+	bool initial_side_slice = mix(clip_box_min, clip_box_max, ray.origin)[slice_axis] > slice_coordinate;
+#endif
 	int istep = 0;
 	for(istep; istep < NUM_STEPS; ++istep) {
 		float t = istep * step_size;
@@ -411,7 +423,6 @@ void main() {
 
 		// apply the transfer function
 		vec4 color_in = apply_transfer_function(density);
-
 	#if ISOSURFACE_MODE > 0
 		#if ISOSURFACE_MODE == 1
 			bool is_isosurface = density >= isovalue;
@@ -446,7 +457,6 @@ void main() {
 	#if ENABLE_GRADIENT_MODULATION == 1
 		opacity_modulation = pow(gradient_length, gradient_lambda);
 	#endif
-
 	#if ISOSURFACE_MODE > 0
 		if(is_isosurface) {
 			#if ISOSURFACE_COLOR_MODE == 0
@@ -463,22 +473,35 @@ void main() {
 			break;
 		}
 	#endif
-
+	#if SLICE_MODE > 0
+		bool at_slice = ((uvw[slice_axis] > slice_coordinate) != initial_side_slice);
+		if (at_slice) {
+	#if SLICE_MODE == 1
+			color_in.a = 1.0;
+	#else
+			color_in.a = slice_opacity;
+	#endif
+			initial_side_slice = !initial_side_slice;
+		}
+		else {
+	#endif
 	#if ENABLE_LIGHTING == 1
-		color_in.rgb = apply_lighting(color_in.rgb, illumination);
+			color_in.rgb = apply_lighting(color_in.rgb, illumination);
 	#endif
 
-		// apply opacity modulation as determined by gradient length if enabled
-		color_in.a *= opacity_modulation;
+			// apply opacity modulation as determined by gradient length if enabled
+			color_in.a *= opacity_modulation;
 
-		color_in.a = -exp(-step_size * scale_adjustment_factor * color_in.a) + 1.0;
-
+			color_in.a = -exp(-step_size * scale_adjustment_factor * color_in.a) + 1.0;
+	#if SLICE_MODE > 0
+		}
+	#endif
 		// premultiply alpha
 		color_in.rgb *= color_in.a;
 
 		// blend front-to-back
-		color.rgb = color.a*color_in.rgb + color.rgb;
-		color.a = (1.0 - color_in.a)*color.a;
+		color.rgb += color.a*color_in.rgb;
+		color.a *= (1.0 - color_in.a);
 
 		// early termination when transparency threshold is reached
 	#if ENABLE_ISOSURFACE == 0
@@ -487,7 +510,11 @@ void main() {
 			break;
 		}
 	#endif
-
+	#if SLICE_MODE == 1
+		if (at_slice) {
+			break;
+		}
+	#endif
 #endif
 	}
 

libs/cgv_gl/volume_renderer.cxx

@@ -48,6 +48,11 @@ namespace cgv {
 			isosurface_color = rgb(0.7f);
 			isosurface_color_from_transfer_function = false;
 
+			slice_mode = SM_DISABLED;
+			slice_axis = 2;
+			slice_coordinate = 0.5f;
+			slice_opacity = 0.5f;
+
 			clip_box = box3(vec3(0.0f), vec3(1.0f));
 		}
 
@@ -114,6 +119,8 @@ namespace cgv {
 			shader_code::set_define(defines, "ISOSURFACE_MODE", vrs.isosurface_mode, volume_render_style::IM_NONE);
 			shader_code::set_define(defines, "ISOSURFACE_COLOR_MODE", vrs.isosurface_color_from_transfer_function, false);
 
+			shader_code::set_define(defines, "SLICE_MODE", vrs.slice_mode, volume_render_style::SM_DISABLED);
+
 			shader_code::set_define(defines, "COMPOSITING_MODE", vrs.compositing_mode, volume_render_style::CM_BLEND);
 			if(transfer_function_texture)
 				shader_code::set_define(defines, "TRANSFER_FUNCTION_SAMPLER_DIMENSIONS", transfer_function_texture->get_nr_dimensions(), 1u);
@@ -218,6 +225,10 @@ namespace cgv {
 			ref_prog().set_uniform(ctx, "isovalue", vrs.isovalue);
 			ref_prog().set_uniform(ctx, "isosurface_color", vrs.isosurface_color);
 
+			ref_prog().set_uniform(ctx, "slice_axis", vrs.slice_axis);
+			ref_prog().set_uniform(ctx, "slice_coordinate", vrs.slice_coordinate);
+			ref_prog().set_uniform(ctx, "slice_opacity", vrs.slice_opacity);
+
 			ref_prog().set_uniform(ctx, "clip_box_min", vrs.clip_box.get_min_pnt());
 			ref_prog().set_uniform(ctx, "clip_box_max", vrs.clip_box.get_max_pnt());
 
@@ -321,6 +332,15 @@ namespace cgv {
 					p->align("\b");
 					p->end_tree_node(vrs_ptr->enable_gradient_modulation);
 				}
+				if (p->begin_tree_node("Orthogonal Slicing", vrs_ptr->slice_mode, false)) {
+					p->align("\a");
+					p->add_member_control(b, "Mode", vrs_ptr->slice_mode, "dropdown", "enums='Disabled,Opaque,Transparent'");
+					p->add_member_control(b, "Axis", vrs_ptr->slice_axis, "value_slider", "min=0;max=2;ticks=true");
+					p->add_member_control(b, "Coordinate", vrs_ptr->slice_coordinate, "value_slider", "min=0;max=1;ticks=true");
+					p->add_member_control(b, "Opacity", vrs_ptr->slice_opacity, "value_slider", "min=0;max=1;ticks=true");
+					p->align("\b");
+					p->end_tree_node(vrs_ptr->slice_mode);
+				}
 
 				if(p->begin_tree_node("Isosurface (Blend only)", vrs_ptr->isosurface_mode, false)) {
 					p->align("\a");

libs/cgv_gl/volume_renderer.h

@@ -91,6 +91,19 @@ namespace cgv { // @<
 			/// whether to color the isosurface based on the transfer function
 			bool isosurface_color_from_transfer_function;
 
+			/// mode of slice rendering
+			enum SliceMode {
+				SM_DISABLED = 0,   // no slice
+				SM_OPAQUE = 1,     // opaque slice rendering
+				SM_TRANSPARENT = 2 // transparent slice rendering 
+			} slice_mode;
+			/// coordinate axis orthogonal to which slice is rendered
+			int   slice_axis;
+			/// coordinate value along axis defining slice in range [0,1]
+			float slice_coordinate;
+			/// in case of transparent mode, slice opacity
+			float slice_opacity;
+
 			/// a bounding box used to define a subspace of the volume to be visualized
 			box3 clip_box;
 

plugins/examples/volume_rendering.cxx

@@ -18,7 +18,7 @@ namespace cgv {
 	}
 }
 
-volume_viewer::volume_viewer() : application_plugin("Volume Viewer")
+volume_viewer::volume_viewer() : application_plugin("Volume Viewer"), depth_tex("[D]")
 {
 	// setup volume bounding box as unit cube centered around origin
 	volume_bounding_box = box3(vec3(-0.5f), vec3(0.5f));
@@ -32,7 +32,11 @@ volume_viewer::volume_viewer() : application_plugin("Volume Viewer")
 	volume_tex.set_wrap_r(cgv::render::TW_CLAMP_TO_BORDER);
 	volume_tex.set_border_color(0.0f, 0.0f, 0.0f, 0.0f);
 
-	vstyle.enable_depth_test = false;
+	// an extra depth texture is used to enable mixing of opaque geometry and the volume
+	depth_tex.set_min_filter(cgv::render::TF_NEAREST);
+	depth_tex.set_mag_filter(cgv::render::TF_NEAREST);
+
+	vstyle.enable_depth_test = true;
 
 	show_box = true;
 
@@ -174,26 +178,41 @@ void volume_viewer::init_frame(cgv::render::context& ctx) {
 				transfer_function_legend_ptr->set_color_map(ctx, transfer_function);
 		}
 	}
+	if (depth_tex.is_created() && (ctx.get_width() != depth_tex.get_width() || ctx.get_height() != depth_tex.get_height()))
+		depth_tex.destruct(ctx);
+
+	if (!depth_tex.is_created())
+		depth_tex.create(ctx, cgv::render::TT_2D, ctx.get_width(), ctx.get_height());
 }
 
-void volume_viewer::draw(cgv::render::context& ctx) 
+void volume_viewer::draw(cgv::render::context& ctx)
 {
 	// default render style for the bounding box
 	static const cgv::render::box_wire_render_style box_rs;
 
 	// render the wireframe bounding box if enabled
-	if(show_box)
+	if (show_box)
 		box_rd.render(ctx, cgv::render::ref_box_wire_renderer(ctx), box_rs);
 
+}
+
+void volume_viewer::after_finish(cgv::render::context & ctx)
+{
+	if (!view_ptr)
+		return;
+
+	// copy the contents of the depth buffer from the opaque geometry into the extra depth texture
+	depth_tex.replace_from_buffer(ctx, 0, 0, 0, 0, ctx.get_width(), ctx.get_height());
+
 	// render the volume
 	auto& vr = cgv::render::ref_volume_renderer(ctx);
 	vr.set_render_style(vstyle);
 	vr.set_volume_texture(&volume_tex); // set volume texture as 3D scalar input data
 	vr.set_transfer_function_texture(&transfer_function.ref_texture()); // get the texture from the transfer function color map to transform scalar volume values into RGBA colors
 	// set the volume bounding box and enable transform to automatically place and size the volume to the defined bounds
 	vr.set_bounding_box(volume_bounding_box);
+	vr.set_depth_texture(&depth_tex);
 	vr.transform_to_bounding_box(true);
-
 	vr.render(ctx, 0, 0);
 }
 
@@ -640,4 +659,4 @@ void volume_viewer::create_histogram() {
 
 #include <cgv/base/register.h>
 
-cgv::base::factory_registration<volume_viewer> volume_viewer_fac("New/Render/Volume Rendering");
+cgv::base::factory_registration<volume_viewer> volume_viewer_fac("Volume Rendering", "shortcut='Ctrl-Alt-V';menu_text='New/Render/Volume Rendering'", true);

plugins/examples/volume_rendering.h

@@ -25,7 +25,7 @@ class volume_viewer :
 	cgv::app::color_map_editor_ptr transfer_function_editor_ptr;
 	cgv::app::color_map_legend_ptr transfer_function_legend_ptr;
 
-	/// resolution of the volume
+		/// resolution of the volume
 	uvec3 vres;
 	/// spacing of the voxels
 	vec3 vspacing;
@@ -36,7 +36,8 @@ class volume_viewer :
 	std::vector<float> vol_data;
 	box3 volume_bounding_box;
 	cgv::render::texture volume_tex;
-
+	cgv::render::texture depth_tex;
+
 
 	// Render members
 	/// store a pointer to the view
@@ -88,6 +89,7 @@ class volume_viewer :
 	bool init(cgv::render::context& ctx);
 	void init_frame(cgv::render::context& ctx);
 	void draw(cgv::render::context& ctx);
+	void after_finish(cgv::render::context& ctx);
 
 	// interface of provider
 	void create_gui();