Rewrite greyscale OpenGL system to use GLSL

Add ability to blend color and greyscale based on window alpha (actual window alpha currently set at 0.5 when blending is enabled)
Reenable greyscale logout effect when compositor is in use

3 files changed, 326 insertions, 103 deletions

diff --git a/twin/compton-tde/common.h b/twin/compton-tde/common.h
index 759e64698..9ff5a2148 100644
--- a/twin/compton-tde/common.h
+++ b/twin/compton-tde/common.h
@@ -490,6 +490,21 @@ typedef struct {
 } glx_blur_cache_t;
 
 typedef struct {
+  /// Fragment shader for greyscale.
+  GLuint frag_shader;
+  /// GLSL program for greyscale.
+  GLuint prog;
+  /// Location of uniform "greyscale_weights" in greyscale GLSL program.
+  GLint unifm_greyscale_weights;
+  /// Location of uniform "enable_blend" in greyscale GLSL program.
+  GLint unifm_enable_blend;
+  /// Location of uniform "tex_scr" in greyscale GLSL program.
+  GLint unifm_tex_scr;
+  /// Location of uniform "alpha_scr" in greyscale GLSL program.
+  GLint unifm_alpha_scr;
+} glx_greyscale_t;
+
+typedef struct {
   /// Framebuffer used for greyscale conversion.
   GLuint fbo;
   /// Textures used for greyscale conversion.
@@ -817,6 +832,9 @@ typedef struct {
 #ifdef CONFIG_VSYNC_OPENGL_GLSL
   glx_blur_pass_t blur_passes[MAX_BLUR_PASS];
 #endif
+#ifdef CONFIG_VSYNC_OPENGL_GLSL
+  glx_greyscale_t greyscale_glsl;
+#endif
 } glx_session_t;
 
 #define CGLX_SESSION_INIT { .context = NULL }
@@ -1068,6 +1086,8 @@ typedef struct _session_t {
   Atom atom_win_type_tde_transparent_to_desktop;
   /// Atom of property <code>_TDE_TRANSPARENCY_FILTER_GREYSCALE</code>.
   Atom atom_win_type_tde_transparency_filter_greyscale;
+  /// Atom of property <code>_TDE_TRANSPARENCY_FILTER_GREYSCALE_BLEND</code>.
+  Atom atom_win_type_tde_transparency_filter_greyscale_blend;
   /// Array of atoms of all possible window types.
   Atom atoms_wintypes[NUM_WINTYPES];
   /// Linked list of additional atoms to track.
@@ -1263,6 +1283,11 @@ typedef struct _win {
   /// Background state on last paint.
   bool greyscale_background_last;
 
+  /// Whether to set window background to blended greyscale.
+  bool greyscale_blended_background;
+  /// Blended greyscale alpha divisor.
+  int greyscale_blended_background_alpha_divisor;
+
   /// Whether to show black background
   bool show_black_background;
 
@@ -2202,6 +2227,9 @@ glx_on_root_change(session_t *ps);
 bool
 glx_init_blur(session_t *ps);
 
+bool
+glx_init_greyscale(session_t *ps);
+
 #ifdef CONFIG_VSYNC_OPENGL_GLSL
 bool
 glx_load_prog_main(session_t *ps,
@@ -2245,7 +2273,7 @@ glx_dim_dst(session_t *ps, int dx, int dy, int width, int height, float z,
 
 bool
 glx_greyscale_dst(session_t *ps, int dx, int dy, int width, int height, float z,
-    XserverRegion reg_tgt, const reg_data_t *pcache_reg, glx_greyscale_cache_t *pbc);
+    glx_texture_t *ptex, XserverRegion reg_tgt, const reg_data_t *pcache_reg, glx_greyscale_cache_t *pbc);
 
 bool
 glx_render_(session_t *ps, const glx_texture_t *ptex,
@@ -2342,7 +2370,6 @@ free_glx_bc(session_t *ps, glx_blur_cache_t *pbc) {
 static inline void
 free_glx_gc_resize(session_t *ps, glx_greyscale_cache_t *pbc) {
   free_texture_r(ps, &pbc->textures[0]);
-  free_texture_r(ps, &pbc->textures[1]);
   pbc->width = 0;
   pbc->height = 0;
 }
diff --git a/twin/compton-tde/compton.c b/twin/compton-tde/compton.c
index dea363f60..d2095123f 100644
--- a/twin/compton-tde/compton.c
+++ b/twin/compton-tde/compton.c
@@ -944,6 +944,9 @@ static Bool
 determine_window_transparency_filter_greyscale(const session_t *ps, Window w);
 
 static Bool
+determine_window_transparency_filter_greyscale_blended(const session_t *ps, Window w);
+
+static Bool
 determine_window_transparent_to_black(const session_t *ps, Window w);
 
 static Bool
@@ -1590,6 +1593,7 @@ xr_greyscale_dst(session_t *ps, Picture tgt_buffer,
 
   XRenderComposite(ps->dpy, PictOpSrc, ps->black_picture, None,
       tmp_picture, 0, 0, 0, 0, 0, 0, wid, hei);
+
   XRenderComposite(ps->dpy, PictOpHSLLuminosity, tgt_buffer, None,
       tmp_picture, x, y, 0, 0, 0, 0, wid, hei);
 
@@ -1723,7 +1727,7 @@ win_greyscale_background(session_t *ps, win *w, Picture tgt_buffer,
 #ifdef CONFIG_VSYNC_OPENGL_GLSL
     case BKEND_GLX:
       glx_greyscale_dst(ps, x, y, wid, hei, ps->psglx->z - 0.5,
-          reg_paint, pcache_reg, &w->glx_greyscale_cache);
+          NULL, reg_paint, pcache_reg, &w->glx_greyscale_cache);
       break;
 #endif
     default:
@@ -1821,6 +1825,71 @@ win_paint_win(session_t *ps, win *w, XserverRegion reg_paint,
 
   Picture pict = w->paint.pict;
 
+  if (w->greyscale_blended_background) {
+    // Set window background to greyscale
+    switch (ps->o.backend) {
+      case BKEND_XRENDER:
+      case BKEND_XR_GLX_HYBRID:
+        {
+          // Blend here such that 0 window alpha is fully colored and 100 window alpha is fully greyscale
+          // PictOpInReverse is used to copy alpha from the source to the destination while preserving destination color
+          // provided that the source has alpha set to 1 (equivalent of CAIRO_OPERATOR_DEST_IN)
+          const int x = w->a.x;
+          const int y = w->a.y;
+          const int wid = w->widthb;
+          const int hei = w->heightb;
+          XserverRegion reg_clip = reg_paint;
+          Picture tgt_buffer = ps->tgt_buffer.pict;
+
+          // Apply clipping region to save some CPU
+          if (reg_paint) {
+            XserverRegion reg = copy_region(ps, reg_paint);
+            XFixesTranslateRegion(ps->dpy, reg, -x, -y);
+            XFixesSetPictureClipRegion(ps->dpy, pict, 0, 0, reg);
+            free_region(ps, &reg);
+          }
+
+          // Create greyscale version of background
+          Picture greyscale_picture = xr_build_picture(ps, wid, hei, w->pictfmt);
+          XRenderComposite(ps->dpy, PictOpSrc, tgt_buffer, None,
+              greyscale_picture, x, y, 0, 0, 0, 0, wid, hei);
+          win_greyscale_background(ps, w, greyscale_picture, reg_paint, pcache_reg);
+
+          Picture tmp_picture = xr_build_picture(ps, wid, hei, w->pictfmt);
+
+          if (!tmp_picture) {
+            printf_errf("(): Failed to build intermediate Picture.");
+          }
+          else {
+            if (reg_clip && tmp_picture)
+              XFixesSetPictureClipRegion(ps->dpy, tmp_picture, reg_clip, 0, 0);
+
+            // Transfer greyscale picture to temporary picture
+            XRenderComposite(ps->dpy, PictOpSrc, greyscale_picture, None,
+              tmp_picture, 0, 0, 0, 0, 0, 0, wid, hei);
+
+            // Transfer alpha of window to temporary picture
+            XRenderComposite(ps->dpy, PictOpInReverse, pict, None,
+                tmp_picture, 0, 0, 0, 0, 0, 0, wid, hei);
+
+            // Blend greyscale picture over main color buffer
+            XRenderComposite(ps->dpy, PictOpOver, tmp_picture, None, tgt_buffer,
+                0, 0, 0, 0, x, y, wid, hei);
+
+            free_picture(ps, &tmp_picture);
+            free_picture(ps, &greyscale_picture);
+          }
+        }
+        break;
+#ifdef CONFIG_VSYNC_OPENGL
+      case BKEND_GLX:
+        glx_greyscale_dst(ps, x, y, wid, hei, ps->psglx->z - 0.5,
+            w->paint.ptex, reg_paint, pcache_reg, &w->glx_greyscale_cache);
+        break;
+#endif
+    }
+  }
+
   // Invert window color, if required
   if (bkend_use_xrender(ps) && w->invert_color) {
     Picture newpict = xr_build_picture(ps, wid, hei, w->pictfmt);
@@ -1846,7 +1915,12 @@ win_paint_win(session_t *ps, win *w, XserverRegion reg_paint,
     }
   }
 
-  const double dopacity = get_opacity_percent(w);
+  double dopacity = get_opacity_percent(w);
+
+  if (w->greyscale_blended_background) {
+    double scaling_factor = (1.0 / w->greyscale_blended_background_alpha_divisor);
+    dopacity = dopacity * scaling_factor;
+  }
 
   if (!w->frame_opacity) {
     win_render(ps, w, 0, 0, wid, hei, dopacity, reg_paint, pcache_reg, pict);
@@ -2439,6 +2513,7 @@ map_win(session_t *ps, Window id) {
   /* This needs to be here since we don't get PropertyNotify when unmapped */
   w->opacity = wid_get_opacity_prop(ps, w->id, OPAQUE);
   w->greyscale_background = determine_window_transparency_filter_greyscale(ps, id);
+  w->greyscale_blended_background = determine_window_transparency_filter_greyscale_blended(ps, id);
   w->show_root_tile = determine_window_transparent_to_desktop(ps, id);
   w->show_black_background = determine_window_transparent_to_black(ps, id);
 
@@ -2632,6 +2707,28 @@ get_window_transparency_filter_greyscale(const session_t *ps, Window w)
 }
 
 static Bool
+get_window_transparency_filter_greyscale_blended(const session_t *ps, Window w)
+{
+	Atom actual;
+	int format;
+	unsigned long n, left;
+
+	unsigned char *data;
+	int result = XGetWindowProperty (ps->dpy, w, ps->atom_win_type_tde_transparency_filter_greyscale_blend, 0L, 1L, False,
+			XA_ATOM, &actual, &format,
+			&n, &left, &data);
+
+	if (result == Success && data != None && format == 32 )
+	{
+		Atom a;
+		a = *(long*)data;
+		XFree ( (void *) data);
+		return True;
+	}
+	return False;
+}
+
+static Bool
 get_window_transparent_to_desktop(const session_t *ps, Window w)
 {
 	Atom actual;
@@ -2711,6 +2808,41 @@ determine_window_transparency_filter_greyscale (const session_t *ps, Window w)
 }
 
 static Bool
+determine_window_transparency_filter_greyscale_blended (const session_t *ps, Window w)
+{
+	Window       root_return, parent_return;
+	Window      *children = NULL;
+	unsigned int nchildren, i;
+	Bool         type;
+
+	type = get_window_transparency_filter_greyscale_blended (ps, w);
+	if (type == True) {
+		return True;
+	}
+
+	if (!XQueryTree (ps->dpy, w, &root_return, &parent_return, &children,
+				&nchildren))
+	{
+		/* XQueryTree failed. */
+		if (children)
+			XFree ((void *)children);
+		return False;
+	}
+
+	for (i = 0;i < nchildren;i++)
+	{
+		type = determine_window_transparency_filter_greyscale_blended (ps, children[i]);
+		if (type == True)
+			return True;
+	}
+
+	if (children)
+		XFree ((void *)children);
+
+	return False;
+}
+
+static Bool
 determine_window_transparent_to_desktop (const session_t *ps, Window w)
 {
 	Window       root_return, parent_return;
@@ -3449,6 +3581,8 @@ add_win(session_t *ps, Window id, Window prev) {
 
     .blur_background = false,
     .greyscale_background = false,
+    .greyscale_blended_background = false,
+    .greyscale_blended_background_alpha_divisor = 2,
 
     .show_black_background = false,
     .show_root_tile = false,
@@ -6696,6 +6830,7 @@ init_atoms(session_t *ps) {
   ps->atom_win_type_tde_transparent_to_black = get_atom(ps, "_TDE_TRANSPARENT_TO_BLACK");
   ps->atom_win_type_tde_transparent_to_desktop = get_atom(ps, "_TDE_TRANSPARENT_TO_DESKTOP");
   ps->atom_win_type_tde_transparency_filter_greyscale = get_atom(ps, "_TDE_TRANSPARENCY_FILTER_GREYSCALE");
+  ps->atom_win_type_tde_transparency_filter_greyscale_blend = get_atom(ps, "_TDE_TRANSPARENCY_FILTER_GREYSCALE_BLEND");
 }
 
 #ifdef CONFIG_XRANDR
@@ -7136,6 +7271,22 @@ init_filters(session_t *ps) {
     }
   }
 
+  // Greyscale filter
+  switch (ps->o.backend) {
+    case BKEND_XRENDER:
+    case BKEND_XR_GLX_HYBRID:
+      {
+        break;
+      }
+#ifdef CONFIG_VSYNC_OPENGL
+    case BKEND_GLX:
+      {
+        if (!glx_init_greyscale(ps))
+          return false;
+      }
+#endif
+  }
+
   return true;
 }
 
@@ -7666,6 +7817,7 @@ session_init(session_t *ps_old, int argc, char **argv) {
     .atom_win_type_tde_transparent_to_black = None,
     .atom_win_type_tde_transparent_to_desktop = None,
     .atom_win_type_tde_transparency_filter_greyscale = None,
+    .atom_win_type_tde_transparency_filter_greyscale_blend = None,
     .atoms_wintypes = { 0 },
     .track_atom_lst = NULL,
 
diff --git a/twin/compton-tde/opengl.c b/twin/compton-tde/opengl.c
index de485de74..4cbfeb455 100644
--- a/twin/compton-tde/opengl.c
+++ b/twin/compton-tde/opengl.c
@@ -531,6 +531,106 @@ glx_init_blur(session_t *ps) {
 #endif
 }
 
+// RAJJA FIXME
+/**
+ * Initialize GLX greyscale filter.
+ */
+bool
+glx_init_greyscale(session_t *ps) {
+#ifdef CONFIG_VSYNC_OPENGL_GLSL
+  {
+    char *lc_numeric_old = mstrcpy(setlocale(LC_NUMERIC, NULL));
+    // Enforce LC_NUMERIC locale "C" here to make sure decimal point is sane
+    setlocale(LC_NUMERIC, "C");
+
+    // Adapted from http://trac.openscenegraph.org/projects/osg//wiki/Support/Tutorials/ShadersSampleGrayingOut
+    static const char *FRAG_SHADER_GREYSCALE =
+      "#version 110\n"
+      "uniform sampler2D tex_scr;\n"
+      "uniform sampler2D alpha_scr;\n"
+      "uniform int enable_blend;\n"
+      "uniform vec4 greyscale_weights; // [0.3, 0.59, 0.11, 1.0]\n"
+      "\n"
+      "void main( void )\n"
+      "{\n"
+      "    // Fetch the regular RGB texel color from the source texture\n"
+      "    vec4 texel_color = texture2D( tex_scr, gl_TexCoord[0].xy );\n"
+      "\n"
+      "    //\n"
+      "    // Converting to grayscale:\n"
+      "    //\n"
+      "    // Converting an image to grayscale is done by taking a weighted average of\n"
+      "    // the red, green and blue color components. The standard weights for this\n" 
+      "    // type of conversion are (0.30, 0.59, 0.11). Therefore, the gray component\n" 
+      "    // or luminance that we need to compute can be defined as a luminance\n" 
+      "    // filter like so:\n"
+      "    //\n"
+      "    // luminance = 0.30*R + 0.59*G + 0.11*B\n"
+      "    //\n"
+      "    // If we think of our RGB colors as vectors, we can see that this \n"
+      "    // calculation is actually just a dot product.\n"
+      "    //\n"
+      "\n"
+      "    vec4 scaledColor = texel_color * greyscale_weights;\n"
+      "    float luminance = scaledColor.r + scaledColor.g + scaledColor.b;\n"
+      "\n"
+      "    if (enable_blend == 1) {\n"
+      "       // Fetch the regular RGB texel color from the blend texture\n"
+      "       vec4 blend_texel = texture2D( alpha_scr, vec2(gl_TexCoord[0].x, 1.0 - gl_TexCoord[0].y) );\n"
+      "       vec4 grey_pixel = vec4(luminance,luminance,luminance,1);\n"
+      "       gl_FragColor = mix(texel_color, grey_pixel, blend_texel.a);\n"
+      "    }\n"
+      "    else {\n"
+      "       gl_FragColor = vec4(luminance,luminance,luminance,1);\n"
+      "    }\n"
+      "\n"
+      "}";
+
+      glx_greyscale_t *greyscale_glsl = &ps->psglx->greyscale_glsl;
+      greyscale_glsl->frag_shader = glx_create_shader(GL_FRAGMENT_SHADER, FRAG_SHADER_GREYSCALE);
+
+      if (!greyscale_glsl->frag_shader) {
+        printf_errf("(): Failed to create fragment shader.");
+        return false;
+      }
+
+      // Build program
+      greyscale_glsl->prog = glx_create_program(&greyscale_glsl->frag_shader, 1);
+      if (!greyscale_glsl->prog) {
+        printf_errf("(): Failed to create GLSL program.");
+        return false;
+      }
+
+      // Get uniform addresses
+#define P_GET_UNIFM_LOC(name, target) { \
+      greyscale_glsl->target = glGetUniformLocation(greyscale_glsl->prog, name); \
+      if (greyscale_glsl->target < 0) { \
+        printf_errf("(): Failed to get location of uniform '" name "'. Might be troublesome."); \
+      } \
+    }
+
+      P_GET_UNIFM_LOC("greyscale_weights", unifm_greyscale_weights);
+      P_GET_UNIFM_LOC("enable_blend", unifm_enable_blend);
+      P_GET_UNIFM_LOC("tex_scr", unifm_tex_scr);
+      P_GET_UNIFM_LOC("alpha_scr", unifm_alpha_scr);
+
+#undef P_GET_UNIFM_LOC
+
+    // Restore LC_NUMERIC
+    setlocale(LC_NUMERIC, lc_numeric_old);
+    free(lc_numeric_old);
+  }
+
+
+  glx_check_err(ps);
+
+  return true;
+#else
+  printf_errf("(): GLSL support not compiled in. Cannot do greyscale with GLX backend.");
+  return false;
+#endif
+}
+
 #ifdef CONFIG_VSYNC_OPENGL_GLSL
 
 /**
@@ -1387,113 +1487,62 @@ glx_blur_dst_end:
 
 bool
 glx_greyscale_dst(session_t *ps, int dx, int dy, int width, int height, float z,
-    XserverRegion reg_tgt, const reg_data_t *pcache_reg, glx_greyscale_cache_t *pbc) {
+    glx_texture_t *ptex, XserverRegion reg_tgt, const reg_data_t *pcache_reg, glx_greyscale_cache_t *gsc) {
+
+  glx_greyscale_t *greyscale_glsl = &ps->psglx->greyscale_glsl;
+  assert(greyscale_glsl->prog);
+
   bool ret = false;
 
   // Calculate copy region size
   glx_greyscale_cache_t ibc = { .width = 0, .height = 0 };
-  if (!pbc)
-    pbc = &ibc;
+  if (!gsc)
+    gsc = &ibc;
 
 #ifdef DEBUG_GLX
   printf_dbgf("(): %d, %d, %d, %d\n", dx, dy, width, height);
 #endif
 
   // Free textures if size inconsistency discovered
-  if (width != pbc->width || height != pbc->height)
-    free_glx_gc_resize(ps, pbc);
+  if (width != gsc->width || height != gsc->height)
+    free_glx_gc_resize(ps, gsc);
 
-  // Generate FBO and textures if needed
-  if (!pbc->textures[0])
-    pbc->textures[0] = glx_gen_texture(ps, GL_TEXTURE_2D, width, height);
-  GLuint tex_scr1 = pbc->textures[0];
-  pbc->width = width;
-  pbc->height = height;
+  // Generate textures
+  if (!gsc->textures[0])
+    gsc->textures[0] = glx_gen_texture(ps, GL_TEXTURE_2D, width, height);
+  GLuint tex_scr1 = gsc->textures[0];
+  gsc->width = width;
+  gsc->height = height;
 
   if (!tex_scr1) {
     printf_errf("(): Failed to allocate texture.");
     goto glx_greyscale_dst_end;
   }
 
-  // Texture scaling factor
-  GLfloat texfac_x = 1.0f, texfac_y = 1.0f;
-  texfac_x /= width;
-  texfac_y /= height;
-
-  // Greyscale conversion in OpenGL ES taken nearly verbatim from this answer on Stack Overflow: http://stackoverflow.com/a/9690145
-
-  // Enable texture unit 0 to divide RGB values in our texture by 2
-  glActiveTexture(GL_TEXTURE0);
   glEnable(GL_TEXTURE_2D);
+  glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, tex_scr1);
+  if (ptex) {
+    glActiveTexture(GL_TEXTURE1);
+    glBindTexture(GL_TEXTURE_2D, ptex->texture);
+  }
+  glActiveTexture(GL_TEXTURE0);
 
   // Read destination pixels into the GL texture
   glx_copy_region_to_tex(ps, GL_TEXTURE_2D, dx, dy, dx, dy, width, height);
 
-  // Finish setting up texture
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
-  glClientActiveTexture(GL_TEXTURE0);
-
-  // GL_MODULATE is Arg0 * Arg1    
-  glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);
-
-  // Configure Arg0
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_TEXTURE);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
-
-  // Configure Arg1
-  float multipliers[4] = {.5, .5, .5, 0.0};
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_CONSTANT);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);
-  glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, (GLfloat*)&multipliers);
-
-  // Enable texture unit 1 to increase RGB values by .5
-  glActiveTexture(GL_TEXTURE1);
-  glEnable(GL_TEXTURE_2D);
-  glBindTexture(GL_TEXTURE_2D, tex_scr1);
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
-  glClientActiveTexture(GL_TEXTURE1);
-
-  // GL_ADD is Arg0 + Arg1
-  glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_ADD);
-
-  // Configure Arg0
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
-
-  // Configure Arg1
-  GLfloat additions[4] = {.5, .5, .5, 0.0};
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_CONSTANT);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);
-  glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, (GLfloat*)&additions);
+  // Texture scaling factor
+  GLfloat texfac_x = 1.0f, texfac_y = 1.0f;
+  texfac_x /= width;
+  texfac_y /= height;
 
-  // Enable texture combiner 2 to get a DOT3_RGB product of your RGB values
-  glActiveTexture(GL_TEXTURE2);
-  glEnable(GL_TEXTURE_2D);
-  glBindTexture(GL_TEXTURE_2D, tex_scr1);
-  glClientActiveTexture(GL_TEXTURE2);
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
-
-  // GL_DOT3_RGB is 4*((Arg0r - 0.5) * (Arg1r - 0.5) + (Arg0g - 0.5) * (Arg1g - 0.5) + (Arg0b - 0.5) * (Arg1b - 0.5))
-  glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_DOT3_RGB);   
-
-  // Configure Arg0
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
-
-  // Configure Arg1
-  // We want this to adjust our DOT3 by R*0.3 + G*0.59 + B*0.11
-  // So, our actual adjustment will need to take into consideration
-  // the fact that OpenGL will subtract .5 from our Arg1
-  // and we need to also take into consideration that we have divided 
-  // our RGB values by 2 and we are multiplying the entire
-  // DOT3 product by 4
-  // So, for Red adjustment you will get :
-  //    .65 = (4*(0.3))/2 + 0.5  = (0.3/2) + 0.5
-  GLfloat weights[4] = {.65, .795, .555, 1.};
-  glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_CONSTANT);
-  glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);
-  glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, (GLfloat*)&weights);
+//   glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
+  glUseProgram(greyscale_glsl->prog);
+  // These coefficients exactly match the non-GL greyscale conversion which uses the XRender PictOpHSLLuminosity operation
+  glUniform4f(greyscale_glsl->unifm_greyscale_weights, 0.3, 0.59, 0.11, 1.0);
+  glUniform1i(greyscale_glsl->unifm_enable_blend, ((ptex)?1:0));
+  glUniform1i(greyscale_glsl->unifm_tex_scr, 0);
+  glUniform1i(greyscale_glsl->unifm_alpha_scr, 1);
 
   // Render!
   {
@@ -1527,26 +1576,21 @@ glx_greyscale_dst(session_t *ps, int dx, int dy, int width, int height, float z,
     P_PAINTREG_END();
   }
 
-  glEnd();
-
-  // Clean up by disabling your texture combiners or texture units.
-  glActiveTexture(GL_TEXTURE2);
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
-  glDisable(GL_TEXTURE_2D);
-
-  glActiveTexture(GL_TEXTURE1);
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
-  glDisable(GL_TEXTURE_2D);
-
-  glActiveTexture(GL_TEXTURE0);
-  glClientActiveTexture(GL_TEXTURE0);
-  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
+  glUseProgram(0);
 
   ret = true;
 
 glx_greyscale_dst_end:
-  if (&ibc == pbc) {
-    free_glx_gc(ps, pbc);
+  if (ptex) {
+    glActiveTexture(GL_TEXTURE1);
+    glBindTexture(GL_TEXTURE_2D, 0);
+  }
+  glActiveTexture(GL_TEXTURE0);
+  glBindTexture(GL_TEXTURE_2D, 0);
+  glDisable(GL_TEXTURE_2D);
+
+  if (&ibc == gsc) {
+    free_glx_gc(ps, gsc);
   }
 
   glx_check_err(ps);