Start working on solid trails for smoke etc.

The implementation is based on
http://codeflow.org/entries/2012/aug/05/webgl-rendering-of-solid-trails/

The shaders have been written and compile and link. The next step is to
generate some data for them.

libs/video/renderer/glsl/Makefile.am

@@ -3,8 +3,8 @@ AUTOMAKE_OPTIONS= foreign
 AM_CFLAGS= @PREFER_PIC@
 AM_CPPFLAGS= -I$(top_srcdir)/include $(GLX_CFLAGS)
 
-shader_src= quakeforge.glsl
+shader_src= quakeforge.glsl trail.frag trail.vert
-shader_gen= quakeforge.slc
+shader_gen= quakeforge.slc trail.fc trail.vc
 
 glsl_src = \
 	glsl_alias.c glsl_bsp.c glsl_draw.c glsl_fog.c glsl_iqm.c glsl_lightmap.c \

libs/video/renderer/glsl/glsl_particles.c

@@ -106,6 +106,14 @@ static const char *particle_textured_frag_effects[] =
 	0
 };
 
+static const char trail_vert[] =
+#include "trail.vc"
+;
+
+static const char trail_frag[] =
+#include "trail.fc"
+;
+
 static struct {
 	int         program;
 	shaderparam_t mvp_matrix;
@@ -140,6 +148,32 @@ static struct {
 	{"fog", 1},
 };
 
+static struct {
+	int         program;
+	shaderparam_t proj;
+	shaderparam_t view;
+	shaderparam_t viewport;
+	shaderparam_t width;
+	shaderparam_t last;
+	shaderparam_t current;
+	shaderparam_t next;
+	shaderparam_t barycentric;
+	shaderparam_t texoff;
+	shaderparam_t smoke;
+} trail = {
+	0,
+	{"proj", 1},
+	{"view", 1},
+	{"viewport", 1},
+	{"width", 1},
+	{"last", 0},
+	{"current", 0},
+	{"next", 0},
+	{"barycentric", 0},
+	{"texoff", 0},
+	{"smoke", 1},
+};
+
 inline static void
 particle_new (ptype_t type, int texnum, const vec3_t org, float scale,
 			  const vec3_t vel, float die, int color, float alpha, float ramp)
@@ -267,6 +301,20 @@ glsl_R_InitParticles (void)
 	GLSL_FreeShader (vert_shader);
 	GLSL_FreeShader (frag_shader);
 
+	vert = GLSL_CompileShader ("trail.vert", trail_vert, GL_VERTEX_SHADER);
+	frag = GLSL_CompileShader ("trail.frag", trail_frag, GL_FRAGMENT_SHADER);
+	trail.program = GLSL_LinkProgram ("trail", vert, frag);
+	GLSL_ResolveShaderParam (trail.program, &trail.proj);
+	GLSL_ResolveShaderParam (trail.program, &trail.view);
+	GLSL_ResolveShaderParam (trail.program, &trail.viewport);
+	GLSL_ResolveShaderParam (trail.program, &trail.width);
+	GLSL_ResolveShaderParam (trail.program, &trail.last);
+	GLSL_ResolveShaderParam (trail.program, &trail.current);
+	GLSL_ResolveShaderParam (trail.program, &trail.next);
+	GLSL_ResolveShaderParam (trail.program, &trail.barycentric);
+	GLSL_ResolveShaderParam (trail.program, &trail.texoff);
+	GLSL_ResolveShaderParam (trail.program, &trail.smoke);
+
 	memset (data, 0, sizeof (data));
 	qfeglGenTextures (1, &part_tex);
 	qfeglBindTexture (GL_TEXTURE_2D, part_tex);

libs/video/renderer/glsl/trail.frag

@@ -0,0 +1,10 @@
+uniform sampler2D smoke;
+
+varying vec2 texcoord;
+varying vec3 vBC;
+
+void
+main (void)
+{
+	gl_FragColor = texture2D (smoke, texcoord) * vec4 (1.0, 1.0, 1.0, 0.7);
+}

libs/video/renderer/glsl/trail.vert

@@ -0,0 +1,68 @@
+attribute vec4 last, current, next;
+attribute vec3 barycentric;
+attribute float texoff;
+
+uniform mat4 proj, view;
+uniform vec2 viewport;
+uniform float width;
+
+varying vec2 texcoord;
+varying vec3 vBC;
+
+vec4
+transform (vec3 coord)
+{
+	return proj * view * vec4 (coord, 1.0);
+}
+
+vec2
+project (vec4 coord)
+{
+	vec3        device = coord.xyz / coord.w;
+	vec2        clip = (device * 0.5 + 0.5).xy;
+	return clip * viewport;
+}
+
+vec4
+unproject (vec2 screen, float z, float w)
+{
+	vec2        clip = screen / viewport;
+	vec2        device = clip * 2.0 - 1.0;
+	return vec4 (device * w, z, w);
+}
+
+float
+estimateScale (vec3 position, vec2 sPosition)
+{
+	vec4        view_pos = view * vec4 (position, 1.0);
+	vec4        scale_pos = view_pos - vec4 (normalize (view_pos.xy) * width,
+											 0.0, 0.0);
+	vec2        screen_scale_pos = project (proj * scale_pos);
+	return distance (sPosition, screen_scale_pos);
+}
+
+void
+main (void)
+{
+	vec2        sLast = project (transform (last.xyz));
+	vec2        sNext = project (transform (next.xyz));
+	vec4        dCurrent = transform (current.xyz);
+	vec2        sCurrent = project (dCurrent);
+	float       off = current.w;
+
+	texcoord = vec2 (texoff * 0.7, off * 0.5 + 0.5);
+	vBC = barycentric;
+
+	// FIXME either n1 or n2 could be zero
+	vec2        n1 = normalize (sLast - sCurrent);
+	vec2        n2 = normalize (sCurrent - sNext);
+	// FIXME if n1 == -n2, the vector will be zero
+	vec2        n = normalize (n1 + n2);
+
+	// rotate the normal by 90 degrees and scale by the desired width
+	vec2        dir = vec2 (n.y, -n.x) * off;
+	float       scale = estimateScale (current.xyz, sCurrent);
+	vec2        pos = sCurrent + dir * scale;
+
+	gl_Position = unproject (pos, dCurrent.z, dCurrent.w);
+}