Fix #44: ghosting on intel. GL_LINES_ADJACENCY errors.

See added comments in sardrawrunway.c.

Basically there is an opengl error message on my intel hardware worst of all
some runway elements are ghosting all over the screen as soon as we run a
ground contact check (which switches gl rendering mode to GL_SELECT for a
frame).

This workaround disables rendering those elements during GL_SELECT. It seems
to work mostly fine. I'm unsure that the issue is in the game but who knows.

src/sardrawrunway.c

@@ -85,9 +85,30 @@ void SARDrawRunway(
 		y_min, y_max,
 		yt_min, yt_max;
 	sar_position_struct cam_pos_runway;
+
 	if((length <= 0.0f) || (width <= 0.0f))
 	    return;
 
+	/* We will be skipping the drawing of some elements when rendering
+	   with GL_SELECT as it triggers ghosting of these elements (they are
+	   drawn and not removed anymore on subsequent frames). This is only
+	   done for ground contact check and these elements (thresholds,
+	   midway markers, touchdown markers, north-south text...) are not
+	   relevant objects. Under GL_SELECT an error is thrown sometimes on
+	   my intel hardware:
+
+	   "HW GL_SELECT does not support draw mode GL_LINES_ADJACENCY"
+
+	   GL_LINES_ADJACENCY must be internally use by the OpenGL
+	   implementation but ghosting also happens without it
+	   sometimes.. This appears to affect only runway elements. I am not
+	   sure why it doesn't affect Helipad or anything else
+	   apparently... *shrug*. This can well be a manifestation of a Mesa
+	   OpenGL bug with intel, as I have not found any other cause.
+	*/
+	GLint render_mode;
+	glGetIntegerv(GL_RENDER_MODE, &render_mode);
+	render_mode = GL_RENDER;
 
 	/* Get runway background texture */
 	if(SARIsTextureAllocated(scene, tex_num))
@@ -190,7 +211,7 @@ void SARDrawRunway(
 
 	    /* Draw north displaced threshold? */
 	    vmodel = runway->north_displaced_threshold_vmodel;
-	    if(vmodel != NULL)
+	    if(vmodel != NULL && render_mode != GL_SELECT)
 	    {
 		glPushMatrix();
 		{
@@ -207,7 +228,7 @@ void SARDrawRunway(
 	    }
 	    /* Draw south displaced threshold? */
 	    vmodel = runway->south_displaced_threshold_vmodel;
-	    if(vmodel != NULL)
+	    if(vmodel != NULL && render_mode != GL_SELECT)
 	    {
 		glPushMatrix();
 		{
@@ -272,7 +293,7 @@ void SARDrawRunway(
 
 	    /* Draw touchdown markers */
 	    vmodel = runway->td_marker_vmodel;
-	    if(vmodel != NULL)
+	    if(vmodel != NULL && render_mode != GL_SELECT)
 	    {
 		glPushMatrix();
 		{
@@ -299,7 +320,7 @@ void SARDrawRunway(
 
 	    /* Draw midway markers */
 	    vmodel = runway->midway_marker_vmodel;
-	    if(vmodel != NULL)
+	    if(vmodel != NULL && render_mode != GL_SELECT)
 	    {
 		glPushMatrix();
 		{
@@ -326,7 +347,7 @@ void SARDrawRunway(
 
 	    /* Draw threshold */
 	    vmodel = runway->threshold_vmodel;
-	    if(vmodel != NULL)
+	    if(vmodel != NULL && render_mode != GL_SELECT)
 	    {
 		glPushMatrix();
 		{
@@ -406,7 +427,8 @@ void SARDrawRunway(
 	    /* Draw north label? */
 	    vmodel = runway->north_label_vmodel;
 	    if((vmodel != NULL) &&
-	       (runway->north_label_width > 0.0f)
+	       (runway->north_label_width > 0.0f) &&
+	       render_mode != GL_SELECT
 	    )
 	    {
 		float label_width = runway->north_label_width;
@@ -427,7 +449,8 @@ void SARDrawRunway(
 	    /* Draw south label? */
 	    vmodel = runway->south_label_vmodel;
 	    if((vmodel != NULL) &&
-	       (runway->south_label_width > 0.0f)
+	       (runway->south_label_width > 0.0f) &&
+	       render_mode != GL_SELECT
 	    )
 	    {
 		float label_width = runway->south_label_width;