Mesa (hw_gl_select): Implement HW accelerated GL_SELECT

Alex Deucher agd5f at kemper.freedesktop.org
Thu Aug 25 09:21:39 PDT 2011


Module: Mesa
Branch: hw_gl_select
Commit: eac31ea1367d1ab1a100513fbbee24a831a8d4e0
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=eac31ea1367d1ab1a100513fbbee24a831a8d4e0

Author: Micael Dias <kam1kaz3 at gmail.com>
Date:   Thu Aug  4 14:59:06 2011 +0100

Implement HW accelerated GL_SELECT

---

 src/mesa/SConscript                          |    1 +
 src/mesa/main/fbobject.c                     |   16 +-
 src/mesa/main/fbobject.h                     |    6 +
 src/mesa/sources.mak                         |    1 +
 src/mesa/state_tracker/st_cb_feedback.c      |   21 +-
 src/mesa/state_tracker/st_context.h          |   10 +
 src/mesa/state_tracker/st_draw.h             |   17 +
 src/mesa/state_tracker/st_draw_select_emul.c |  490 ++++++++++++++++++++++++++
 8 files changed, 549 insertions(+), 13 deletions(-)

diff --git a/src/mesa/SConscript b/src/mesa/SConscript
index b0c3334..d37457b 100644
--- a/src/mesa/SConscript
+++ b/src/mesa/SConscript
@@ -262,6 +262,7 @@ statetracker_sources = [
     'state_tracker/st_debug.c',
     'state_tracker/st_draw.c',
     'state_tracker/st_draw_feedback.c',
+    'state_tracker/st_draw_select_emul.c',
     'state_tracker/st_extensions.c',
     'state_tracker/st_format.c',
     'state_tracker/st_glsl_to_tgsi.cpp',
diff --git a/src/mesa/main/fbobject.c b/src/mesa/main/fbobject.c
index 0b48fc7..68dfa08 100644
--- a/src/mesa/main/fbobject.c
+++ b/src/mesa/main/fbobject.c
@@ -1560,8 +1560,8 @@ _mesa_IsFramebufferEXT(GLuint framebuffer)
  * (render to texture).  Call ctx->Driver.RenderTexture() for such
  * attachments.
  */
-static void
-check_begin_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb)
+void
+_mesa_check_begin_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb)
 {
    GLuint i;
    ASSERT(ctx->Driver.RenderTexture);
@@ -1583,8 +1583,8 @@ check_begin_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb)
  * If so, call ctx->Driver.FinishRenderTexture() for each texture to
  * notify the device driver that the texture image may have changed.
  */
-static void
-check_end_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb)
+void
+_mesa_check_end_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb)
 {
    if (is_winsys_fbo(fb))
       return; /* can't render to texture with winsys framebuffers */
@@ -1713,7 +1713,7 @@ _mesa_BindFramebufferEXT(GLenum target, GLuint framebuffer)
       FLUSH_VERTICES(ctx, _NEW_BUFFERS);
 
       /* check if old readbuffer was render-to-texture */
-      check_end_texture_render(ctx, oldReadFb);
+      _mesa_check_end_texture_render(ctx, oldReadFb);
 
       _mesa_reference_framebuffer(&ctx->ReadBuffer, newReadFb);
    }
@@ -1723,13 +1723,13 @@ _mesa_BindFramebufferEXT(GLenum target, GLuint framebuffer)
 
       /* check if old read/draw buffers were render-to-texture */
       if (!bindReadBuf)
-         check_end_texture_render(ctx, oldReadFb);
+         _mesa_check_end_texture_render(ctx, oldReadFb);
 
       if (oldDrawFb != oldReadFb)
-         check_end_texture_render(ctx, oldDrawFb);
+         _mesa_check_end_texture_render(ctx, oldDrawFb);
 
       /* check if newly bound framebuffer has any texture attachments */
-      check_begin_texture_render(ctx, newDrawFb);
+      _mesa_check_begin_texture_render(ctx, newDrawFb);
 
       _mesa_reference_framebuffer(&ctx->DrawBuffer, newDrawFb);
    }
diff --git a/src/mesa/main/fbobject.h b/src/mesa/main/fbobject.h
index 7eb2005..ca6251c 100644
--- a/src/mesa/main/fbobject.h
+++ b/src/mesa/main/fbobject.h
@@ -101,6 +101,12 @@ _mesa_is_legal_color_format(const struct gl_context *ctx, GLenum baseFormat);
 extern GLenum
 _mesa_base_fbo_format(struct gl_context *ctx, GLenum internalFormat);
 
+extern void
+_mesa_check_begin_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb);
+
+extern void
+_mesa_check_end_texture_render(struct gl_context *ctx, struct gl_framebuffer *fb);
+
 extern GLboolean GLAPIENTRY
 _mesa_IsRenderbufferEXT(GLuint renderbuffer);
 
diff --git a/src/mesa/sources.mak b/src/mesa/sources.mak
index 5e77e0f..6c158c6 100644
--- a/src/mesa/sources.mak
+++ b/src/mesa/sources.mak
@@ -229,6 +229,7 @@ STATETRACKER_SOURCES = \
 	state_tracker/st_debug.c \
 	state_tracker/st_draw.c \
 	state_tracker/st_draw_feedback.c \
+	state_tracker/st_draw_select_emul.c \
 	state_tracker/st_extensions.c \
 	state_tracker/st_format.c \
 	state_tracker/st_gen_mipmap.c \
diff --git a/src/mesa/state_tracker/st_cb_feedback.c b/src/mesa/state_tracker/st_cb_feedback.c
index 9b85a39..c96c97c 100644
--- a/src/mesa/state_tracker/st_cb_feedback.c
+++ b/src/mesa/state_tracker/st_cb_feedback.c
@@ -276,17 +276,28 @@ st_RenderMode(struct gl_context *ctx, GLenum newMode )
 {
    struct st_context *st = st_context(ctx);
    struct draw_context *draw = st->draw;
+   bool hw_acc_path = _mesa_getenv("MESA_HW_SELECT") && !st->select_emul.hw_unsupported;
 
    if (newMode == GL_RENDER) {
       /* restore normal VBO draw function */
       vbo_set_draw_func(ctx, st_draw_vbo);
    }
    else if (newMode == GL_SELECT) {
-      if (!st->selection_stage)
-         st->selection_stage = draw_glselect_stage(ctx, draw);
-      draw_set_rasterize_stage(draw, st->selection_stage);
-      /* Plug in new vbo draw function */
-      vbo_set_draw_func(ctx, st_feedback_draw_vbo);
+      if (hw_acc_path) {
+         if (st_select_emul_begin(ctx)) {
+            vbo_set_draw_func(ctx, st_select_draw_func);
+         }
+         else {
+            hw_acc_path = false;
+         }
+      }
+      if (!hw_acc_path) {
+         if (!st->selection_stage)
+            st->selection_stage = draw_glselect_stage(ctx, draw);
+         draw_set_rasterize_stage(draw, st->selection_stage);
+         /* Plug in new vbo draw function */
+         vbo_set_draw_func(ctx, st_feedback_draw_vbo);
+      }
    }
    else {
       if (!st->feedback_stage)
diff --git a/src/mesa/state_tracker/st_context.h b/src/mesa/state_tracker/st_context.h
index 0a32202..8a8e11a 100644
--- a/src/mesa/state_tracker/st_context.h
+++ b/src/mesa/state_tracker/st_context.h
@@ -207,6 +207,16 @@ struct st_context
 
    int32_t draw_stamp;
    int32_t read_stamp;
+
+   /* data related to hw accelerated GL_SELECT */
+   struct gl_selection_emul
+   {
+      GLboolean hw_unsupported;
+      struct gl_framebuffer *fbo;
+      GLuint rb_depth_name;
+      GLuint rb_color_name;
+      void *fs;
+   } select_emul;
 };
 
 
diff --git a/src/mesa/state_tracker/st_draw.h b/src/mesa/state_tracker/st_draw.h
index a7b50ce..d27e321 100644
--- a/src/mesa/state_tracker/st_draw.h
+++ b/src/mesa/state_tracker/st_draw.h
@@ -87,5 +87,22 @@ pointer_to_offset(const void *ptr)
    return (unsigned) (((unsigned long) ptr) & 0xffffffffUL);
 }
 
+/* Functions used by the hw accelerated GL_SELECT emulator
+ */
+extern bool
+st_select_emul_begin(struct gl_context *ctx);
+
+extern void
+st_select_emul_end(struct gl_context *ctx);
+
+extern void
+st_select_draw_func(struct gl_context *ctx,
+            const struct gl_client_array **arrays,
+            const struct _mesa_prim *prims,
+            GLuint nr_prims,
+            const struct _mesa_index_buffer *ib,
+            GLboolean index_bounds_valid,
+            GLuint min_index,
+            GLuint max_index);
 
 #endif
diff --git a/src/mesa/state_tracker/st_draw_select_emul.c b/src/mesa/state_tracker/st_draw_select_emul.c
new file mode 100644
index 0000000..d6bb244
--- /dev/null
+++ b/src/mesa/state_tracker/st_draw_select_emul.c
@@ -0,0 +1,490 @@
+/**************************************************************************
+ * 
+ * Copyright 2011 Micael Dias <kam1kaz3 (at) gmail (dot) com>,
+ *                Pierre-Eric Pelloux-Prayer
+ * All Rights Reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sub license, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ * 
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial portions
+ * of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
+ * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ * 
+ **************************************************************************/
+
+/**
+ * This file contains code that attempts to accelerate GL_SELECT rendering.
+ * It was created with the intent of solving the following bug:
+ *     https://bugs.freedesktop.org/show_bug.cgi?id=34495
+ *
+ * This code is a rewritten version of the patch "GL_SELECT hw support v5"
+ * posted by user Pierre-Eric Pelloux-Prayer in the previously mentioned bug.
+ *
+ * In order to test this code, the env. variable MESA_HW_SELECT should be
+ * exported.
+ *
+ * How this algorithm works:
+ * - When in GL_SELECT mode, draw calls are redirected to st_select_draw_func()
+ * which configures states in a way that makes the rendered primitives draw
+ * to a custom FBO that stores depth values (both min and max values) and
+ * emits these values through _mesa_update_hitflag().
+ */
+
+#include "main/imports.h"
+#include "main/image.h"
+#include "main/macros.h"
+#include "main/mfeatures.h"
+#include "main/hash.h"
+
+#include "main/context.h"
+#include "main/enable.h"
+#include "main/fbobject.h"
+#include "main/depth.h"
+#include "main/state.h"
+#include "main/scissor.h"
+#include "main/viewport.h"
+#include "main/framebuffer.h"
+#include "main/feedback.h"
+
+#include "vbo/vbo.h"
+
+#include "st_context.h"
+#include "st_atom.h"
+#include "st_cb_bufferobjects.h"
+#include "st_draw.h"
+#include "st_program.h"
+#include "st_texture.h"
+#include "st_cb_readpixels.h"
+
+#include "pipe/p_context.h"
+#include "pipe/p_defines.h"
+#include "pipe/p_state.h"
+#include "pipe/p_format.h"
+#include "pipe/p_shader_tokens.h"
+#include "util/u_inlines.h"
+#include "util/u_simple_shaders.h"
+#include "cso_cache/cso_context.h"
+#include "tgsi/tgsi_ureg.h"
+
+#include "draw/draw_private.h"
+#include "draw/draw_context.h"
+
+/**
+ * Custom fragment shader that does nothing but ouput a constant color
+ */
+static void*
+st_select_emul_create_fs(struct gl_context *ctx)
+{
+   struct st_context *st = st_context(ctx);
+   struct pipe_context *pipe = st->pipe;
+   struct ureg_program *ureg;
+   struct ureg_dst out;
+   struct ureg_src imm;
+
+   ureg = ureg_create( TGSI_PROCESSOR_FRAGMENT );
+   if (ureg == NULL)
+      return NULL;
+
+   out = ureg_DECL_output( ureg,
+                           TGSI_SEMANTIC_COLOR,
+                           0 );
+
+   imm = ureg_imm4f( ureg, 0.0f, 0.0f, 0.0f, 1.0f );
+
+   ureg_MOV( ureg, out, imm );
+   ureg_END( ureg );
+
+   return ureg_create_shader_and_destroy( ureg, pipe );
+}
+
+/**
+ * Clears the depth values of our FBO by setting the
+ * 1st pixel to 1.0f and the 2nd to 0.0f
+ */
+static void
+st_select_emul_clear_fbo(struct gl_context *ctx)
+{
+   struct st_context *st = st_context(ctx);
+   struct gl_scissor_attrib saved_scissor;
+   struct gl_framebuffer *saved_fbo = NULL;
+   GLfloat clearDepth;
+
+   /* save states */
+   saved_scissor = ctx->Scissor;
+   if (ctx->DrawBuffer) {
+      _mesa_reference_framebuffer(&saved_fbo, ctx->DrawBuffer);
+   }
+   clearDepth = ctx->Depth.Clear;
+
+   /* hack needed because Clear does nothing if render mode != GL_RENDER */
+   ctx->RenderMode = GL_RENDER;
+   
+   /* disable old draw fbo */
+   if (saved_fbo) {
+      /* XXX: needs flushing? */
+      _mesa_check_end_texture_render(ctx, saved_fbo);
+   }
+
+   /* use our fbo */
+   _mesa_check_begin_texture_render(ctx, st->select_emul.fbo);
+   _mesa_reference_framebuffer(&ctx->DrawBuffer, st->select_emul.fbo);
+
+   /* update fbo */
+   _mesa_update_framebuffer(ctx);
+
+   /* make sure context is up to date */
+   _mesa_update_state(ctx);
+
+   /* enable scissor */
+   ctx->Scissor.Enabled = GL_TRUE;
+
+   /* clear min-Z */
+   ctx->Scissor.X = 0;
+   ctx->Scissor.Y = 0;
+   ctx->Scissor.Width = 1;
+   ctx->Scissor.Height = 1;
+   ctx->Depth.Clear = 1.0f;
+   if (ctx->Driver.ClearDepth)
+      (*ctx->Driver.ClearDepth)(ctx, ctx->Depth.Clear);
+   ctx->NewState |= _NEW_SCISSOR | _NEW_DEPTH | _NEW_BUFFERS;
+   _mesa_update_state(ctx);
+   ctx->Driver.Clear(ctx, BUFFER_BIT_DEPTH);
+
+   /* clear max-Z */
+   ctx->Scissor.X = 1;
+   ctx->Scissor.Y = 0;
+   ctx->Scissor.Width = 1;
+   ctx->Scissor.Height = 1;
+   ctx->Depth.Clear = 0.0f;
+   if (ctx->Driver.ClearDepth)
+      (*ctx->Driver.ClearDepth)(ctx, ctx->Depth.Clear);
+   ctx->NewState |= _NEW_SCISSOR | _NEW_DEPTH;
+   _mesa_update_state(ctx);
+   ctx->Driver.Clear(ctx, BUFFER_BIT_DEPTH);
+
+   /* restore states */
+   _mesa_check_end_texture_render(ctx, st->select_emul.fbo);
+   if (saved_fbo) {
+      _mesa_check_begin_texture_render(ctx, saved_fbo);
+      _mesa_reference_framebuffer(&ctx->DrawBuffer, saved_fbo);
+      _mesa_reference_framebuffer(&saved_fbo, NULL);
+   }
+   else
+      _mesa_reference_framebuffer(&ctx->DrawBuffer, NULL);
+
+   ctx->RenderMode = GL_SELECT;
+   ctx->Depth.Clear = clearDepth;
+   if (ctx->Driver.ClearDepth)
+      (*ctx->Driver.ClearDepth)(ctx, ctx->Depth.Clear);
+   ctx->Scissor = saved_scissor;
+   ctx->NewState |= _NEW_SCISSOR | _NEW_DEPTH | _NEW_BUFFERS;
+   _mesa_update_state(ctx);
+}
+
+/**
+ * Clean up data
+ */
+static void
+st_select_emul_destroy_fbo(struct gl_context *ctx)
+{
+   struct st_context *st = st_context(ctx);
+   if (st->select_emul.rb_color_name) {
+      _mesa_DeleteRenderbuffersEXT(1, &st->select_emul.rb_color_name);
+      st->select_emul.rb_color_name = 0;
+   }
+   if (st->select_emul.rb_depth_name) {
+      _mesa_DeleteRenderbuffersEXT(1, &st->select_emul.rb_depth_name);
+      st->select_emul.rb_depth_name = 0;
+   }
+   if (st->select_emul.fbo) {
+      _mesa_DeleteFramebuffersEXT(1, &st->select_emul.fbo->Name);
+      _mesa_reference_framebuffer(&st->select_emul.fbo, NULL);
+   }
+   if (st->select_emul.fs) {
+      cso_delete_fragment_shader(st->cso_context, st->select_emul.fs);
+      st->select_emul.fs = NULL;
+   }
+}
+
+/**
+ * Create and setup FBO needed for our operations
+ */
+static bool
+st_select_emul_create_fbo(struct gl_context *ctx)
+{
+   GLuint fboName;
+   struct st_context *st = st_context(ctx);
+
+   /* make sure we don't leak memory */
+   st_select_emul_destroy_fbo(ctx);
+
+   /* create buffer names */
+   _mesa_GenFramebuffersEXT(1, &fboName);
+   _mesa_GenRenderbuffersEXT(1, &st->select_emul.rb_depth_name);
+   _mesa_GenRenderbuffersEXT(1, &st->select_emul.rb_color_name);
+
+   /* allocate buffers' memory */
+   _mesa_BindFramebufferEXT(GL_FRAMEBUFFER, fboName);
+   _mesa_BindRenderbufferEXT(GL_RENDERBUFFER, st->select_emul.rb_depth_name);
+   _mesa_RenderbufferStorageEXT(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, 2, 1);
+   _mesa_BindRenderbufferEXT(GL_RENDERBUFFER, st->select_emul.rb_color_name);
+   _mesa_RenderbufferStorageEXT(GL_RENDERBUFFER, GL_RGBA, 2, 1);
+   _mesa_BindRenderbufferEXT(GL_RENDERBUFFER, 0);
+
+   /* setup fbo */
+   _mesa_FramebufferRenderbufferEXT(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
+                                    GL_RENDERBUFFER,
+                                    st->select_emul.rb_depth_name);
+   _mesa_FramebufferRenderbufferEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                                    GL_RENDERBUFFER,
+                                    st->select_emul.rb_color_name);
+
+   if (_mesa_CheckFramebufferStatusEXT(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+      st_select_emul_destroy_fbo(ctx);
+      return false;
+   }
+
+   _mesa_BindFramebufferEXT(GL_FRAMEBUFFER, 0);
+
+   /* get fbo pointer */
+   st->select_emul.fbo = _mesa_lookup_framebuffer(ctx, fboName);
+
+   /* create fragment shader */
+   st->select_emul.fs = st_select_emul_create_fs(ctx);
+
+   /* check fbo pointer validity */
+   if (!st->select_emul.fbo) {
+      st_select_emul_destroy_fbo(ctx);
+      return false;
+   }
+
+   return true;
+}
+
+/**
+ * Called when entering GL_SELECT mode.
+ * This function initializes our private data and clears
+ * depth so that the next draw call will have it ready.
+ */
+bool
+st_select_emul_begin(struct gl_context *ctx)
+{
+   struct st_context *st = st_context(ctx);
+
+   /* perform an hw caps check once */
+   static bool hw_checked = false;
+   if (!hw_checked) {
+      hw_checked = true;
+      /* XXX: is this a proper way to check for hw support? */
+      if (!ctx->Driver.ReadPixels ||
+          !ctx->Driver.DrawPixels ||
+          !ctx->Driver.NewFramebuffer ||
+          !ctx->Driver.NewRenderbuffer) {
+         st->select_emul.hw_unsupported = true;
+         return false;
+      }
+   }
+
+   /* initialize fbo if not yet initialized */
+   if (!st->select_emul.fbo) {
+      if (!st_select_emul_create_fbo(ctx)) {
+         return false;
+      }
+   }
+   
+   /* clear FBO */
+   st_select_emul_clear_fbo(ctx);
+
+   return true;
+}
+
+void
+st_select_emul_end(struct gl_context *ctx)
+{
+   st_select_emul_destroy_fbo(ctx);
+}
+
+/**
+ * Reads into our FBO and emit z-buffer results
+ * called by st_select_draw_func()
+ */
+static void
+st_select_emul_update_hits(struct gl_context *ctx)
+{
+   struct st_context *st = st_context(ctx);
+   struct gl_framebuffer *saved_fbo = NULL;
+   float zData[2];
+
+   /* set state */
+   if (ctx->ReadBuffer) {
+      _mesa_reference_framebuffer(&saved_fbo, ctx->ReadBuffer);
+      _mesa_check_end_texture_render(ctx, saved_fbo);
+   }
+   _mesa_check_begin_texture_render(ctx, st->select_emul.fbo);
+   _mesa_reference_framebuffer(&ctx->ReadBuffer, st->select_emul.fbo);
+
+   /* update fbo */
+   _mesa_update_framebuffer( ctx );
+  
+   /* update state */
+   ctx->NewState |= _NEW_BUFFERS;
+   _mesa_update_state( ctx );
+
+   /* read pixels */
+   ctx->Driver.ReadPixels( ctx, 0, 0, 2, 1,
+                           GL_DEPTH_COMPONENT, GL_FLOAT,
+                           &ctx->Pack, (void*)zData );
+
+   /* emit z-buffer results */
+   if (zData[0] != 1.0f)
+      _mesa_update_hitflag( ctx, zData[0] );
+   if (zData[1] != 0.0f)
+      _mesa_update_hitflag( ctx, zData[1] );
+
+   /* clear FBO */
+   st_select_emul_clear_fbo(ctx);
+
+   /* restore state */
+   _mesa_check_end_texture_render(ctx, st->select_emul.fbo);
+   if (saved_fbo) {
+      _mesa_check_begin_texture_render(ctx, saved_fbo);
+      _mesa_reference_framebuffer(&ctx->ReadBuffer, saved_fbo);
+      _mesa_reference_framebuffer(&saved_fbo, NULL);
+   }
+   else
+      _mesa_reference_framebuffer(&ctx->ReadBuffer, NULL);
+
+   /* update state */
+   ctx->NewState |= _NEW_BUFFERS;
+   _mesa_update_state( ctx );
+}
+
+/**
+ * Plug in draw function to draw in GL_SELECT mode.
+ * This function does the following steps:
+ *   1) render into the 1st pixel of our FBO with depth state
+ *      configured so that we get the lowest Z values
+ *   2) render into the 2nd pixel of our FBO with depth state
+ *      configured so that we get the highest Z values
+ *   3) calls st_select_emul_update_hits() to emit results
+ */
+void
+st_select_draw_func(struct gl_context *ctx,
+                    const struct gl_client_array **arrays,
+                    const struct _mesa_prim *prims,
+                    GLuint nr_prims,
+                    const struct _mesa_index_buffer *ib,
+                    GLboolean index_bounds_valid,
+                    GLuint min_index,
+                    GLuint max_index)
+{
+   GLboolean saved_scissorEnabled;
+   struct gl_framebuffer *saved_fbo = NULL;
+   struct st_context *st = st_context(ctx);
+   struct pipe_depth_stencil_alpha_state state_depth;
+   struct pipe_viewport_state state_viewport;
+
+   /* save states */
+   if (ctx->DrawBuffer)
+      _mesa_reference_framebuffer(&saved_fbo, ctx->DrawBuffer);
+
+   saved_scissorEnabled = ctx->Scissor.Enabled;
+   cso_save_fragment_shader(st->cso_context);
+   cso_save_depth_stencil_alpha(st->cso_context);
+   cso_save_viewport(st->cso_context);
+   
+   /* prepare stencil state */
+   memset(&state_depth, 0, sizeof(state_depth));
+   state_depth.depth.enabled = 1;
+   state_depth.depth.writemask = 1;
+
+   /* prepare viewport state */
+   memset(&state_viewport, 0, sizeof(state_viewport));
+   state_viewport.scale[0] = 0.5f * 2.0f * 0.5;
+   state_viewport.scale[1] = 0.5f * 1.0f;
+   state_viewport.scale[2] = 1.0f;
+   state_viewport.scale[3] = 1.0f;
+   state_viewport.translate[1] = 0.5f * 1.0f;
+   state_viewport.translate[2] = 0.0f;
+   state_viewport.translate[3] = 0.0f;
+
+   /* use our custom fragment shader */
+   cso_set_fragment_shader_handle(st->cso_context, st->select_emul.fs);
+
+   /* disable scissor */
+   ctx->Scissor.Enabled = GL_FALSE;
+
+   /* disable old draw fbo */
+   if (saved_fbo)
+      _mesa_check_end_texture_render(ctx, saved_fbo);
+
+   /* use our fbo */
+   _mesa_check_begin_texture_render(ctx, st->select_emul.fbo);
+   _mesa_reference_framebuffer(&ctx->DrawBuffer, st->select_emul.fbo);
+
+   /* update fbo */
+   _mesa_update_framebuffer( ctx );
+   
+   /* update context */
+   _mesa_update_state(ctx);
+
+   /* render min-z */
+   {
+      /* specific states */
+      state_depth.depth.func = PIPE_FUNC_LESS;
+      state_viewport.translate[0] = 0.5f * 1.0f + 0.0f;
+
+      cso_set_depth_stencil_alpha(st->cso_context, &state_depth);
+      cso_set_viewport(st->cso_context, &state_viewport);
+
+      /* draw */
+      st_draw_vbo(ctx, arrays, prims, nr_prims, ib, index_bounds_valid, min_index, max_index);
+   }
+
+   /* render max-z */
+   {
+      state_depth.depth.func = PIPE_FUNC_GREATER;
+      state_viewport.translate[0] = 0.5f * 1.0f + 1.0f;
+
+      cso_set_depth_stencil_alpha(st->cso_context, &state_depth);
+      cso_set_viewport(st->cso_context, &state_viewport);
+
+      /* draw */
+      st_draw_vbo(ctx, arrays, prims, nr_prims, ib, index_bounds_valid, min_index, max_index);
+   }
+
+   /* XXX: needs flushing? */
+
+   /* restore states */
+   cso_restore_fragment_shader(st->cso_context);
+   cso_restore_depth_stencil_alpha(st->cso_context);
+   cso_restore_viewport(st->cso_context);
+   ctx->Scissor.Enabled = saved_scissorEnabled;
+   _mesa_check_end_texture_render(ctx, st->select_emul.fbo);
+   if (saved_fbo) {
+      _mesa_check_begin_texture_render(ctx, saved_fbo);
+      _mesa_reference_framebuffer(&ctx->DrawBuffer, saved_fbo);
+      _mesa_reference_framebuffer(&saved_fbo, NULL);
+   }
+   else
+      _mesa_reference_framebuffer(&ctx->DrawBuffer, NULL);
+   _mesa_update_state(ctx);
+
+   /* update hits */
+   st_select_emul_update_hits(ctx);
+}
+



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