Apply clipping planes to passthrough shader

This adds support for using clipping planes with the passthrough shader
by passing through the clip equation of the specified plane and then
using gl_ClipDistance for using the built-in clipping capabilities.

Author: asarium

.editorconfig

@@ -2,3 +2,6 @@ root = true
 
 [*.{h,cpp}]
 indent_style = tab
+
+[*.sdr]
+indent_style = tab

code/def_files/passthrough-v.sdr

@@ -6,9 +6,18 @@ out vec4 fragColor;
 uniform mat4 modelViewMatrix;
 uniform mat4 projMatrix;
 uniform vec4 color;
+
+uniform mat4 modelMatrix;
+uniform bool clipEnabled;
+uniform vec4 clipEquation;
+
 void main()
 {
 	fragTexCoord = vertTexCoord;
 	fragColor = vertColor * color;
 	gl_Position = projMatrix * modelViewMatrix * vertPosition;
-}
+
+	if (clipEnabled) {
+		gl_ClipDistance[0] = dot(clipEquation, modelMatrix * vertPosition);
+	}
+}

code/graphics/opengl/gropenglshader.cpp

@@ -106,7 +106,7 @@ static opengl_shader_type_t GL_shader_types[] = {
 		{ opengl_vert_attrib::POSITION, opengl_vert_attrib::TEXCOORD }, "Video Playback" },
 
 	{ SDR_TYPE_PASSTHROUGH_RENDER, "passthrough-v.sdr", "passthrough-f.sdr", 0,
-		{ "modelViewMatrix", "projMatrix", "baseMap", "noTexturing", "alphaTexture", "srgb", "intensity", "color", "alphaThreshold" },
+		{ "modelViewMatrix", "projMatrix", "baseMap", "noTexturing", "alphaTexture", "srgb", "intensity", "color", "alphaThreshold", "clipEnabled", "clipEquation", "modelMatrix" },
 		{ opengl_vert_attrib::POSITION, opengl_vert_attrib::TEXCOORD, opengl_vert_attrib::COLOR }, "Passthrough" },
 
 	{ SDR_TYPE_SHIELD_DECAL, "shield-impact-v.sdr",	"shield-impact-f.sdr", 0,
@@ -788,7 +788,7 @@ void opengl_shader_compile_passthrough_shader()
 	opengl_shader_set_current();
 }
 
-void opengl_shader_set_passthrough(bool textured, bool alpha, vec4 *clr, float color_scale)
+void opengl_shader_set_passthrough(bool textured, bool alpha, vec4 *clr, float color_scale, const material::clip_plane& clip_plane)
 {
 	opengl_shader_set_current(gr_opengl_maybe_create_shader(SDR_TYPE_PASSTHROUGH_RENDER, 0));
 
@@ -820,6 +820,21 @@ void opengl_shader_set_passthrough(bool textured, bool alpha, vec4 *clr, float c
 		Current_shader->program->Uniforms.setUniform4f("color", 1.0f, 1.0f, 1.0f, 1.0f);
 	}
 
+	if (clip_plane.enabled) {
+		Current_shader->program->Uniforms.setUniformi("clipEnabled", 1);
+
+		vec4 clip_equation;
+		clip_equation.xyzw.x = clip_plane.normal.xyz.x;
+		clip_equation.xyzw.y = clip_plane.normal.xyz.y;
+		clip_equation.xyzw.z = clip_plane.normal.xyz.z;
+		clip_equation.xyzw.w = -vm_vec_dot(&clip_plane.normal, &clip_plane.position);
+
+		Current_shader->program->Uniforms.setUniform4f("clipEquation", clip_equation);
+		Current_shader->program->Uniforms.setUniformMatrix4f("modelMatrix", GL_model_matrix_stack.get_transform());
+	} else {
+		Current_shader->program->Uniforms.setUniformi("clipEnabled", 0);
+	}
+
 	Current_shader->program->Uniforms.setUniformMatrix4f("modelViewMatrix", GL_model_view_matrix);
 	Current_shader->program->Uniforms.setUniformMatrix4f("projMatrix", GL_projection_matrix);
 }

code/graphics/opengl/gropenglshader.h

@@ -14,6 +14,7 @@
 #include "globalincs/pstypes.h"
 #include "graphics/2d.h"
 #include "graphics/opengl/gropengl.h"
+#include "graphics/material.h"
 #include "ShaderProgram.h"
 
 #include <string>
@@ -166,7 +167,7 @@ void opengl_shader_compile_deferred_light_shader();
 void opengl_shader_compile_deferred_light_clear_shader();
 
 void opengl_shader_compile_passthrough_shader();
-void opengl_shader_set_passthrough(bool textured = true, bool alpha = false, vec4* clr = NULL, float color_scale = 1.0f);
+void opengl_shader_set_passthrough(bool textured = true, bool alpha = false, vec4* clr = NULL, float color_scale = 1.0f, const material::clip_plane& clip_plane = material::clip_plane());
 void opengl_shader_set_passthrough(bool textured, bool alpha, color *clr);
 
 #define ANIMATED_SHADER_LOADOUTSELECT_FS1	0

code/graphics/opengl/gropengltnl.cpp

@@ -796,7 +796,9 @@ void gr_opengl_set_clip_plane(vec3d *clip_normal, vec3d *clip_point)
 	if ( clip_normal == NULL || clip_point == NULL ) {
 		GL_state.ClipDistance(0, false);
 	} else {
-		Assertion(Current_shader != NULL && Current_shader->shader == SDR_TYPE_MODEL, "Clip planes are only supported by the model shader!");
+		Assertion(Current_shader != NULL &&
+				  (Current_shader->shader == SDR_TYPE_MODEL || Current_shader->shader == SDR_TYPE_PASSTHROUGH_RENDER),
+				  "Clip planes are not supported by this shader!");
 
 		GL_state.ClipDistance(0, true);
 	}
@@ -863,10 +865,6 @@ void opengl_tnl_set_material(material* material_info, bool set_base_map)
 
 	opengl_shader_set_current(shader_handle);
 
-	if ( Current_shader->shader == SDR_TYPE_PASSTHROUGH_RENDER ) {
-		opengl_shader_set_passthrough(base_map >= 0, material_info->get_texture_type() == TCACHE_TYPE_AABITMAP, &clr, material_info->get_color_scale());
-	}
-
 	GL_state.SetAlphaBlendMode(material_info->get_blend_mode());
 	GL_state.SetZbufferType(material_info->get_depth_mode());
 
@@ -894,6 +892,14 @@ void opengl_tnl_set_material(material* material_info, bool set_base_map)
 		gr_opengl_set_clip_plane(NULL, NULL);
 	}
 
+	if ( Current_shader->shader == SDR_TYPE_PASSTHROUGH_RENDER ) {
+		opengl_shader_set_passthrough(base_map >= 0,
+									  material_info->get_texture_type() == TCACHE_TYPE_AABITMAP,
+									  &clr,
+									  material_info->get_color_scale(),
+									  material_info->get_clip_plane());
+	}
+
 	if ( set_base_map && base_map >= 0 ) {
 		float u_scale, v_scale;
 

code/graphics/opengl/gropengltnl.h

@@ -33,6 +33,7 @@ extern float shadow_middist;
 extern float shadow_fardist;
 extern bool Rendering_to_shadow_map;
 
+extern transform_stack GL_model_matrix_stack;
 extern matrix4 GL_view_matrix;
 extern matrix4 GL_model_view_matrix;
 extern matrix4 GL_projection_matrix;