i965: Map GL_PATCHES to 3DPRIM_PATCHLIST_n.

[mesa.git] / src / mesa / drivers / dri / i965 / brw_draw.c

/*
 * Copyright 2003 VMware, Inc.
 * 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, sublicense, 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 NONINFRINGEMENT.
 * IN NO EVENT SHALL VMWARE 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.
 */

#include <sys/errno.h>

#include "main/glheader.h"
#include "main/context.h"
#include "main/condrender.h"
#include "main/samplerobj.h"
#include "main/state.h"
#include "main/enums.h"
#include "main/macros.h"
#include "main/transformfeedback.h"
#include "main/framebuffer.h"
#include "tnl/tnl.h"
#include "vbo/vbo_context.h"
#include "swrast/swrast.h"
#include "swrast_setup/swrast_setup.h"
#include "drivers/common/meta.h"

#include "brw_blorp.h"
#include "brw_draw.h"
#include "brw_defines.h"
#include "brw_context.h"
#include "brw_state.h"
#include "brw_vs.h"

#include "intel_batchbuffer.h"
#include "intel_buffers.h"
#include "intel_fbo.h"
#include "intel_mipmap_tree.h"
#include "intel_buffer_objects.h"

#define FILE_DEBUG_FLAG DEBUG_PRIMS

static const GLuint prim_to_hw_prim[GL_TRIANGLE_STRIP_ADJACENCY+1] = {
   [GL_POINTS] =_3DPRIM_POINTLIST,
   [GL_LINES] = _3DPRIM_LINELIST,
   [GL_LINE_LOOP] = _3DPRIM_LINELOOP,
   [GL_LINE_STRIP] = _3DPRIM_LINESTRIP,
   [GL_TRIANGLES] = _3DPRIM_TRILIST,
   [GL_TRIANGLE_STRIP] = _3DPRIM_TRISTRIP,
   [GL_TRIANGLE_FAN] = _3DPRIM_TRIFAN,
   [GL_QUADS] = _3DPRIM_QUADLIST,
   [GL_QUAD_STRIP] = _3DPRIM_QUADSTRIP,
   [GL_POLYGON] = _3DPRIM_POLYGON,
   [GL_LINES_ADJACENCY] = _3DPRIM_LINELIST_ADJ,
   [GL_LINE_STRIP_ADJACENCY] = _3DPRIM_LINESTRIP_ADJ,
   [GL_TRIANGLES_ADJACENCY] = _3DPRIM_TRILIST_ADJ,
   [GL_TRIANGLE_STRIP_ADJACENCY] = _3DPRIM_TRISTRIP_ADJ,
};


static const GLenum reduced_prim[GL_POLYGON+1] = {
   [GL_POINTS] = GL_POINTS,
   [GL_LINES] = GL_LINES,
   [GL_LINE_LOOP] = GL_LINES,
   [GL_LINE_STRIP] = GL_LINES,
   [GL_TRIANGLES] = GL_TRIANGLES,
   [GL_TRIANGLE_STRIP] = GL_TRIANGLES,
   [GL_TRIANGLE_FAN] = GL_TRIANGLES,
   [GL_QUADS] = GL_TRIANGLES,
   [GL_QUAD_STRIP] = GL_TRIANGLES,
   [GL_POLYGON] = GL_TRIANGLES
};

uint32_t
get_hw_prim_for_gl_prim(int mode)
{
   if (mode >= BRW_PRIM_OFFSET)
      return mode - BRW_PRIM_OFFSET;
   else {
      assert(mode < ARRAY_SIZE(prim_to_hw_prim));
      return prim_to_hw_prim[mode];
   }
}


/* When the primitive changes, set a state bit and re-validate.  Not
 * the nicest and would rather deal with this by having all the
 * programs be immune to the active primitive (ie. cope with all
 * possibilities).  That may not be realistic however.
 */
static void
brw_set_prim(struct brw_context *brw, const struct _mesa_prim *prim)
{
   struct gl_context *ctx = &brw->ctx;
   uint32_t hw_prim = get_hw_prim_for_gl_prim(prim->mode);

   DBG("PRIM: %s\n", _mesa_enum_to_string(prim->mode));

   /* Slight optimization to avoid the GS program when not needed:
    */
   if (prim->mode == GL_QUAD_STRIP &&
       ctx->Light.ShadeModel != GL_FLAT &&
       ctx->Polygon.FrontMode == GL_FILL &&
       ctx->Polygon.BackMode == GL_FILL)
      hw_prim = _3DPRIM_TRISTRIP;

   if (prim->mode == GL_QUADS && prim->count == 4 &&
       ctx->Light.ShadeModel != GL_FLAT &&
       ctx->Polygon.FrontMode == GL_FILL &&
       ctx->Polygon.BackMode == GL_FILL) {
      hw_prim = _3DPRIM_TRIFAN;
   }

   if (hw_prim != brw->primitive) {
      brw->primitive = hw_prim;
      brw->ctx.NewDriverState |= BRW_NEW_PRIMITIVE;

      if (reduced_prim[prim->mode] != brw->reduced_primitive) {
         brw->reduced_primitive = reduced_prim[prim->mode];
         brw->ctx.NewDriverState |= BRW_NEW_REDUCED_PRIMITIVE;
      }
   }
}

static void
gen6_set_prim(struct brw_context *brw, const struct _mesa_prim *prim)
{
   const struct gl_context *ctx = &brw->ctx;
   uint32_t hw_prim;

   DBG("PRIM: %s\n", _mesa_enum_to_string(prim->mode));

   if (prim->mode == GL_PATCHES)
      hw_prim = _3DPRIM_PATCHLIST(ctx->TessCtrlProgram.patch_vertices);
   else
      hw_prim = get_hw_prim_for_gl_prim(prim->mode);

   if (hw_prim != brw->primitive) {
      brw->primitive = hw_prim;
      brw->ctx.NewDriverState |= BRW_NEW_PRIMITIVE;
   }
}


/**
 * The hardware is capable of removing dangling vertices on its own; however,
 * prior to Gen6, we sometimes convert quads into trifans (and quad strips
 * into tristrips), since pre-Gen6 hardware requires a GS to render quads.
 * This function manually trims dangling vertices from a draw call involving
 * quads so that those dangling vertices won't get drawn when we convert to
 * trifans/tristrips.
 */
static GLuint
trim(GLenum prim, GLuint length)
{
   if (prim == GL_QUAD_STRIP)
      return length > 3 ? (length - length % 2) : 0;
   else if (prim == GL_QUADS)
      return length - length % 4;
   else
      return length;
}


static void
brw_emit_prim(struct brw_context *brw,
              const struct _mesa_prim *prim,
              uint32_t hw_prim)
{
   int verts_per_instance;
   int vertex_access_type;
   int indirect_flag;

   DBG("PRIM: %s %d %d\n", _mesa_enum_to_string(prim->mode),
       prim->start, prim->count);

   int start_vertex_location = prim->start;
   int base_vertex_location = prim->basevertex;

   if (prim->indexed) {
      vertex_access_type = brw->gen >= 7 ?
         GEN7_3DPRIM_VERTEXBUFFER_ACCESS_RANDOM :
         GEN4_3DPRIM_VERTEXBUFFER_ACCESS_RANDOM;
      start_vertex_location += brw->ib.start_vertex_offset;
      base_vertex_location += brw->vb.start_vertex_bias;
   } else {
      vertex_access_type = brw->gen >= 7 ?
         GEN7_3DPRIM_VERTEXBUFFER_ACCESS_SEQUENTIAL :
         GEN4_3DPRIM_VERTEXBUFFER_ACCESS_SEQUENTIAL;
      start_vertex_location += brw->vb.start_vertex_bias;
   }

   /* We only need to trim the primitive count on pre-Gen6. */
   if (brw->gen < 6)
      verts_per_instance = trim(prim->mode, prim->count);
   else
      verts_per_instance = prim->count;

   /* If nothing to emit, just return. */
   if (verts_per_instance == 0 && !prim->is_indirect)
      return;

   /* If we're set to always flush, do it before and after the primitive emit.
    * We want to catch both missed flushes that hurt instruction/state cache
    * and missed flushes of the render cache as it heads to other parts of
    * the besides the draw code.
    */
   if (brw->always_flush_cache)
      brw_emit_mi_flush(brw);

   /* If indirect, emit a bunch of loads from the indirect BO. */
   if (prim->is_indirect) {
      struct gl_buffer_object *indirect_buffer = brw->ctx.DrawIndirectBuffer;
      drm_intel_bo *bo = intel_bufferobj_buffer(brw,
            intel_buffer_object(indirect_buffer),
            prim->indirect_offset, 5 * sizeof(GLuint));

      indirect_flag = GEN7_3DPRIM_INDIRECT_PARAMETER_ENABLE;

      brw_load_register_mem(brw, GEN7_3DPRIM_VERTEX_COUNT, bo,
                            I915_GEM_DOMAIN_VERTEX, 0,
                            prim->indirect_offset + 0);
      brw_load_register_mem(brw, GEN7_3DPRIM_INSTANCE_COUNT, bo,
                            I915_GEM_DOMAIN_VERTEX, 0,
                            prim->indirect_offset + 4);

      brw_load_register_mem(brw, GEN7_3DPRIM_START_VERTEX, bo,
                            I915_GEM_DOMAIN_VERTEX, 0,
                            prim->indirect_offset + 8);
      if (prim->indexed) {
         brw_load_register_mem(brw, GEN7_3DPRIM_BASE_VERTEX, bo,
                               I915_GEM_DOMAIN_VERTEX, 0,
                               prim->indirect_offset + 12);
         brw_load_register_mem(brw, GEN7_3DPRIM_START_INSTANCE, bo,
                               I915_GEM_DOMAIN_VERTEX, 0,
                               prim->indirect_offset + 16);
      } else {
         brw_load_register_mem(brw, GEN7_3DPRIM_START_INSTANCE, bo,
                               I915_GEM_DOMAIN_VERTEX, 0,
                               prim->indirect_offset + 12);
         BEGIN_BATCH(3);
         OUT_BATCH(MI_LOAD_REGISTER_IMM | (3 - 2));
         OUT_BATCH(GEN7_3DPRIM_BASE_VERTEX);
         OUT_BATCH(0);
         ADVANCE_BATCH();
      }
   } else {
      indirect_flag = 0;
   }

   BEGIN_BATCH(brw->gen >= 7 ? 7 : 6);

   if (brw->gen >= 7) {
      const int predicate_enable =
         (brw->predicate.state == BRW_PREDICATE_STATE_USE_BIT)
         ? GEN7_3DPRIM_PREDICATE_ENABLE : 0;

      OUT_BATCH(CMD_3D_PRIM << 16 | (7 - 2) | indirect_flag | predicate_enable);
      OUT_BATCH(hw_prim | vertex_access_type);
   } else {
      OUT_BATCH(CMD_3D_PRIM << 16 | (6 - 2) |
                hw_prim << GEN4_3DPRIM_TOPOLOGY_TYPE_SHIFT |
                vertex_access_type);
   }
   OUT_BATCH(verts_per_instance);
   OUT_BATCH(start_vertex_location);
   OUT_BATCH(prim->num_instances);
   OUT_BATCH(prim->base_instance);
   OUT_BATCH(base_vertex_location);
   ADVANCE_BATCH();

   if (brw->always_flush_cache)
      brw_emit_mi_flush(brw);
}


static void
brw_merge_inputs(struct brw_context *brw,
                 const struct gl_client_array *arrays[])
{
   const struct gl_context *ctx = &brw->ctx;
   GLuint i;

   for (i = 0; i < brw->vb.nr_buffers; i++) {
      drm_intel_bo_unreference(brw->vb.buffers[i].bo);
      brw->vb.buffers[i].bo = NULL;
   }
   brw->vb.nr_buffers = 0;

   for (i = 0; i < VERT_ATTRIB_MAX; i++) {
      brw->vb.inputs[i].buffer = -1;
      brw->vb.inputs[i].glarray = arrays[i];
   }

   if (brw->gen < 8 && !brw->is_haswell) {
      struct gl_program *vp = &ctx->VertexProgram._Current->Base;
      /* Prior to Haswell, the hardware can't natively support GL_FIXED or
       * 2_10_10_10_REV vertex formats.  Set appropriate workaround flags.
       */
      for (i = 0; i < VERT_ATTRIB_MAX; i++) {
         if (!(vp->InputsRead & BITFIELD64_BIT(i)))
            continue;

         uint8_t wa_flags = 0;

         switch (brw->vb.inputs[i].glarray->Type) {

         case GL_FIXED:
            wa_flags = brw->vb.inputs[i].glarray->Size;
            break;

         case GL_INT_2_10_10_10_REV:
            wa_flags |= BRW_ATTRIB_WA_SIGN;
            /* fallthough */

         case GL_UNSIGNED_INT_2_10_10_10_REV:
            if (brw->vb.inputs[i].glarray->Format == GL_BGRA)
               wa_flags |= BRW_ATTRIB_WA_BGRA;

            if (brw->vb.inputs[i].glarray->Normalized)
               wa_flags |= BRW_ATTRIB_WA_NORMALIZE;
            else if (!brw->vb.inputs[i].glarray->Integer)
               wa_flags |= BRW_ATTRIB_WA_SCALE;

            break;
         }

         if (brw->vb.attrib_wa_flags[i] != wa_flags) {
            brw->vb.attrib_wa_flags[i] = wa_flags;
            brw->ctx.NewDriverState |= BRW_NEW_VS_ATTRIB_WORKAROUNDS;
         }
      }
   }
}

/**
 * \brief Call this after drawing to mark which buffers need resolving
 *
 * If the depth buffer was written to and if it has an accompanying HiZ
 * buffer, then mark that it needs a depth resolve.
 *
 * If the color buffer is a multisample window system buffer, then
 * mark that it needs a downsample.
 *
 * Also mark any render targets which will be textured as needing a render
 * cache flush.
 */
static void
brw_postdraw_set_buffers_need_resolve(struct brw_context *brw)
{
   struct gl_context *ctx = &brw->ctx;
   struct gl_framebuffer *fb = ctx->DrawBuffer;

   struct intel_renderbuffer *front_irb = NULL;
   struct intel_renderbuffer *back_irb = intel_get_renderbuffer(fb, BUFFER_BACK_LEFT);
   struct intel_renderbuffer *depth_irb = intel_get_renderbuffer(fb, BUFFER_DEPTH);
   struct intel_renderbuffer *stencil_irb = intel_get_renderbuffer(fb, BUFFER_STENCIL);
   struct gl_renderbuffer_attachment *depth_att = &fb->Attachment[BUFFER_DEPTH];

   if (_mesa_is_front_buffer_drawing(fb))
      front_irb = intel_get_renderbuffer(fb, BUFFER_FRONT_LEFT);

   if (front_irb)
      front_irb->need_downsample = true;
   if (back_irb)
      back_irb->need_downsample = true;
   if (depth_irb && ctx->Depth.Mask) {
      intel_renderbuffer_att_set_needs_depth_resolve(depth_att);
      brw_render_cache_set_add_bo(brw, depth_irb->mt->bo);
   }

   if (ctx->Extensions.ARB_stencil_texturing &&
       stencil_irb && ctx->Stencil._WriteEnabled) {
      brw_render_cache_set_add_bo(brw, stencil_irb->mt->bo);
   }

   for (unsigned i = 0; i < fb->_NumColorDrawBuffers; i++) {
      struct intel_renderbuffer *irb =
         intel_renderbuffer(fb->_ColorDrawBuffers[i]);

      if (irb)
         brw_render_cache_set_add_bo(brw, irb->mt->bo);
   }
}

/* May fail if out of video memory for texture or vbo upload, or on
 * fallback conditions.
 */
static void
brw_try_draw_prims(struct gl_context *ctx,
                   const struct gl_client_array *arrays[],
                   const struct _mesa_prim *prims,
                   GLuint nr_prims,
                   const struct _mesa_index_buffer *ib,
                   GLuint min_index,
                   GLuint max_index,
                   struct gl_buffer_object *indirect)
{
   struct brw_context *brw = brw_context(ctx);
   GLuint i;
   bool fail_next = false;

   if (ctx->NewState)
      _mesa_update_state(ctx);

   /* Find the highest sampler unit used by each shader program.  A bit-count
    * won't work since ARB programs use the texture unit number as the sampler
    * index.
    */
   brw->wm.base.sampler_count =
      _mesa_fls(ctx->FragmentProgram._Current->Base.SamplersUsed);
   brw->gs.base.sampler_count = ctx->GeometryProgram._Current ?
      _mesa_fls(ctx->GeometryProgram._Current->Base.SamplersUsed) : 0;
   brw->vs.base.sampler_count =
      _mesa_fls(ctx->VertexProgram._Current->Base.SamplersUsed);

   /* We have to validate the textures *before* checking for fallbacks;
    * otherwise, the software fallback won't be able to rely on the
    * texture state, the firstLevel and lastLevel fields won't be
    * set in the intel texture object (they'll both be 0), and the
    * software fallback will segfault if it attempts to access any
    * texture level other than level 0.
    */
   brw_validate_textures(brw);

   intel_prepare_render(brw);

   /* This workaround has to happen outside of brw_upload_render_state()
    * because it may flush the batchbuffer for a blit, affecting the state
    * flags.
    */
   brw_workaround_depthstencil_alignment(brw, 0);

   /* Bind all inputs, derive varying and size information:
    */
   brw_merge_inputs(brw, arrays);

   brw->ib.ib = ib;
   brw->ctx.NewDriverState |= BRW_NEW_INDICES;

   brw->vb.min_index = min_index;
   brw->vb.max_index = max_index;
   brw->ctx.NewDriverState |= BRW_NEW_VERTICES;

   for (i = 0; i < nr_prims; i++) {
      int estimated_max_prim_size;
      const int sampler_state_size = 16;

      estimated_max_prim_size = 512; /* batchbuffer commands */
      estimated_max_prim_size += BRW_MAX_TEX_UNIT *
         (sampler_state_size + sizeof(struct gen5_sampler_default_color));
      estimated_max_prim_size += 1024; /* gen6 VS push constants */
      estimated_max_prim_size += 1024; /* gen6 WM push constants */
      estimated_max_prim_size += 512; /* misc. pad */

      /* Flush the batch if it's approaching full, so that we don't wrap while
       * we've got validated state that needs to be in the same batch as the
       * primitives.
       */
      intel_batchbuffer_require_space(brw, estimated_max_prim_size, RENDER_RING);
      intel_batchbuffer_save_state(brw);

      if (brw->num_instances != prims[i].num_instances ||
          brw->basevertex != prims[i].basevertex) {
         brw->num_instances = prims[i].num_instances;
         brw->basevertex = prims[i].basevertex;
         if (i > 0) { /* For i == 0 we just did this before the loop */
            brw->ctx.NewDriverState |= BRW_NEW_VERTICES;
            brw_merge_inputs(brw, arrays);
         }
      }

      brw->draw.gl_basevertex =
         prims[i].indexed ? prims[i].basevertex : prims[i].start;

      drm_intel_bo_unreference(brw->draw.draw_params_bo);

      if (prims[i].is_indirect) {
         /* Point draw_params_bo at the indirect buffer. */
         brw->draw.draw_params_bo =
            intel_buffer_object(ctx->DrawIndirectBuffer)->buffer;
         drm_intel_bo_reference(brw->draw.draw_params_bo);
         brw->draw.draw_params_offset =
            prims[i].indirect_offset + (prims[i].indexed ? 12 : 8);
      } else {
         /* Set draw_params_bo to NULL so brw_prepare_vertices knows it
          * has to upload gl_BaseVertex and such if they're needed.
          */
         brw->draw.draw_params_bo = NULL;
         brw->draw.draw_params_offset = 0;
      }

      if (brw->gen < 6)
         brw_set_prim(brw, &prims[i]);
      else
         gen6_set_prim(brw, &prims[i]);

retry:

      /* Note that before the loop, brw->ctx.NewDriverState was set to != 0, and
       * that the state updated in the loop outside of this block is that in
       * *_set_prim or intel_batchbuffer_flush(), which only impacts
       * brw->ctx.NewDriverState.
       */
      if (brw->ctx.NewDriverState) {
         brw->no_batch_wrap = true;
         brw_upload_render_state(brw);
      }

      brw_emit_prim(brw, &prims[i], brw->primitive);

      brw->no_batch_wrap = false;

      if (dri_bufmgr_check_aperture_space(&brw->batch.bo, 1)) {
         if (!fail_next) {
            intel_batchbuffer_reset_to_saved(brw);
            intel_batchbuffer_flush(brw);
            fail_next = true;
            goto retry;
         } else {
            int ret = intel_batchbuffer_flush(brw);
            WARN_ONCE(ret == -ENOSPC,
                      "i965: Single primitive emit exceeded "
                      "available aperture space\n");
         }
      }

      /* Now that we know we haven't run out of aperture space, we can safely
       * reset the dirty bits.
       */
      if (brw->ctx.NewDriverState)
         brw_render_state_finished(brw);
   }

   if (brw->always_flush_batch)
      intel_batchbuffer_flush(brw);

   brw_state_cache_check_size(brw);
   brw_postdraw_set_buffers_need_resolve(brw);

   return;
}

void
brw_draw_prims(struct gl_context *ctx,
               const struct _mesa_prim *prims,
               GLuint nr_prims,
               const struct _mesa_index_buffer *ib,
               GLboolean index_bounds_valid,
               GLuint min_index,
               GLuint max_index,
               struct gl_transform_feedback_object *unused_tfb_object,
               unsigned stream,
               struct gl_buffer_object *indirect)
{
   struct brw_context *brw = brw_context(ctx);
   const struct gl_client_array **arrays = ctx->Array._DrawArrays;

   assert(unused_tfb_object == NULL);

   if (!brw_check_conditional_render(brw))
      return;

   /* Handle primitive restart if needed */
   if (brw_handle_primitive_restart(ctx, prims, nr_prims, ib, indirect)) {
      /* The draw was handled, so we can exit now */
      return;
   }

   /* Do GL_SELECT and GL_FEEDBACK rendering using swrast, even though it
    * won't support all the extensions we support.
    */
   if (ctx->RenderMode != GL_RENDER) {
      perf_debug("%s render mode not supported in hardware\n",
                 _mesa_enum_to_string(ctx->RenderMode));
      _swsetup_Wakeup(ctx);
      _tnl_wakeup(ctx);
      _tnl_draw_prims(ctx, prims, nr_prims, ib,
                      index_bounds_valid, min_index, max_index, NULL, 0, NULL);
      return;
   }

   /* If we're going to have to upload any of the user's vertex arrays, then
    * get the minimum and maximum of their index buffer so we know what range
    * to upload.
    */
   if (!index_bounds_valid && !vbo_all_varyings_in_vbos(arrays)) {
      perf_debug("Scanning index buffer to compute index buffer bounds.  "
                 "Use glDrawRangeElements() to avoid this.\n");
      vbo_get_minmax_indices(ctx, prims, ib, &min_index, &max_index, nr_prims);
   }

   /* Try drawing with the hardware, but don't do anything else if we can't
    * manage it.  swrast doesn't support our featureset, so we can't fall back
    * to it.
    */
   brw_try_draw_prims(ctx, arrays, prims, nr_prims, ib, min_index, max_index,
                      indirect);
}

void
brw_draw_init(struct brw_context *brw)
{
   struct gl_context *ctx = &brw->ctx;
   struct vbo_context *vbo = vbo_context(ctx);

   /* Register our drawing function:
    */
   vbo->draw_prims = brw_draw_prims;

   for (int i = 0; i < VERT_ATTRIB_MAX; i++)
      brw->vb.inputs[i].buffer = -1;
   brw->vb.nr_buffers = 0;
   brw->vb.nr_enabled = 0;
}

void
brw_draw_destroy(struct brw_context *brw)
{
   unsigned i;

   for (i = 0; i < brw->vb.nr_buffers; i++) {
      drm_intel_bo_unreference(brw->vb.buffers[i].bo);
      brw->vb.buffers[i].bo = NULL;
   }
   brw->vb.nr_buffers = 0;

   for (i = 0; i < brw->vb.nr_enabled; i++) {
      brw->vb.enabled[i]->buffer = -1;
   }
   brw->vb.nr_enabled = 0;

   drm_intel_bo_unreference(brw->ib.bo);
   brw->ib.bo = NULL;
}