예제 #1
0
/**
 * Try to do a fast and simple RGB(a) glDrawPixels.
 * Return:  GL_TRUE if success, GL_FALSE if slow path must be used instead
 */
static GLboolean
fast_draw_rgba_pixels(struct gl_context *ctx, GLint x, GLint y,
                      GLsizei width, GLsizei height,
                      GLenum format, GLenum type,
                      const struct gl_pixelstore_attrib *userUnpack,
                      const GLvoid *pixels)
{
   const GLint imgX = x, imgY = y;
   struct gl_renderbuffer *rb = ctx->DrawBuffer->_ColorDrawBuffers[0];
   GLenum rbType;
   SWcontext *swrast = SWRAST_CONTEXT(ctx);
   SWspan span;
   GLboolean simpleZoom;
   GLint yStep;  /* +1 or -1 */
   struct gl_pixelstore_attrib unpack;
   GLint destX, destY, drawWidth, drawHeight; /* post clipping */

   if (!rb)
      return GL_TRUE; /* no-op */

   rbType = rb->DataType;

   if ((swrast->_RasterMask & ~CLIP_BIT) ||
       ctx->Texture._EnabledCoordUnits ||
       userUnpack->SwapBytes ||
       ctx->_ImageTransferState) {
      /* can't handle any of those conditions */
      return GL_FALSE;
   }

   INIT_SPAN(span, GL_BITMAP);
   span.arrayMask = SPAN_RGBA;
   span.arrayAttribs = FRAG_BIT_COL0;
   _swrast_span_default_attribs(ctx, &span);

   /* copy input params since clipping may change them */
   unpack = *userUnpack;
   destX = x;
   destY = y;
   drawWidth = width;
   drawHeight = height;

   /* check for simple zooming and clipping */
   if (ctx->Pixel.ZoomX == 1.0F &&
       (ctx->Pixel.ZoomY == 1.0F || ctx->Pixel.ZoomY == -1.0F)) {
      if (!_mesa_clip_drawpixels(ctx, &destX, &destY,
                                 &drawWidth, &drawHeight, &unpack)) {
         /* image was completely clipped: no-op, all done */
         return GL_TRUE;
      }
      simpleZoom = GL_TRUE;
      yStep = (GLint) ctx->Pixel.ZoomY;
      ASSERT(yStep == 1 || yStep == -1);
   }
   else {
      /* non-simple zooming */
      simpleZoom = GL_FALSE;
      yStep = 1;
      if (unpack.RowLength == 0)
         unpack.RowLength = width;
   }

   /*
    * Ready to draw!
    */

   if (format == GL_RGBA && type == rbType) {
      const GLubyte *src
         = (const GLubyte *) _mesa_image_address2d(&unpack, pixels, width,
                                                   height, format, type, 0, 0);
      const GLint srcStride = _mesa_image_row_stride(&unpack, width,
                                                     format, type);
      if (simpleZoom) {
         GLint row;
         for (row = 0; row < drawHeight; row++) {
            rb->PutRow(ctx, rb, drawWidth, destX, destY, src, NULL);
            src += srcStride;
            destY += yStep;
         }
      }
      else {
         /* with zooming */
         GLint row;
         for (row = 0; row < drawHeight; row++) {
            span.x = destX;
            span.y = destY + row;
            span.end = drawWidth;
            span.array->ChanType = rbType;
            _swrast_write_zoomed_rgba_span(ctx, imgX, imgY, &span, src);
            src += srcStride;
         }
         span.array->ChanType = CHAN_TYPE;
      }
      return GL_TRUE;
   }

   if (format == GL_RGB && type == rbType) {
      const GLubyte *src
         = (const GLubyte *) _mesa_image_address2d(&unpack, pixels, width,
                                                   height, format, type, 0, 0);
      const GLint srcStride = _mesa_image_row_stride(&unpack, width,
                                                     format, type);
      if (simpleZoom) {
         GLint row;
         for (row = 0; row < drawHeight; row++) {
            rb->PutRowRGB(ctx, rb, drawWidth, destX, destY, src, NULL);
            src += srcStride;
            destY += yStep;
         }
      }
      else {
         /* with zooming */
         GLint row;
         for (row = 0; row < drawHeight; row++) {
            span.x = destX;
            span.y = destY;
            span.end = drawWidth;
            span.array->ChanType = rbType;
            _swrast_write_zoomed_rgb_span(ctx, imgX, imgY, &span, src);
            src += srcStride;
            destY++;
         }
         span.array->ChanType = CHAN_TYPE;
      }
      return GL_TRUE;
   }

   /* Remaining cases haven't been tested with alignment != 1 */
   if (userUnpack->Alignment != 1)
      return GL_FALSE;

   if (format == GL_LUMINANCE && type == CHAN_TYPE && rbType == CHAN_TYPE) {
      const GLchan *src = (const GLchan *) pixels
         + (unpack.SkipRows * unpack.RowLength + unpack.SkipPixels);
      if (simpleZoom) {
         /* no zooming */
         GLint row;
         ASSERT(drawWidth <= MAX_WIDTH);
         for (row = 0; row < drawHeight; row++) {
            GLchan rgb[MAX_WIDTH][3];
            GLint i;
            for (i = 0;i<drawWidth;i++) {
               rgb[i][0] = src[i];
               rgb[i][1] = src[i];
               rgb[i][2] = src[i];
            }
            rb->PutRowRGB(ctx, rb, drawWidth, destX, destY, rgb, NULL);
            src += unpack.RowLength;
            destY += yStep;
         }
      }
      else {
         /* with zooming */
         GLint row;
         ASSERT(drawWidth <= MAX_WIDTH);
         for (row = 0; row < drawHeight; row++) {
            GLchan rgb[MAX_WIDTH][3];
            GLint i;
            for (i = 0;i<drawWidth;i++) {
               rgb[i][0] = src[i];
               rgb[i][1] = src[i];
               rgb[i][2] = src[i];
            }
            span.x = destX;
            span.y = destY;
            span.end = drawWidth;
            _swrast_write_zoomed_rgb_span(ctx, imgX, imgY, &span, rgb);
            src += unpack.RowLength;
            destY++;
         }
      }
      return GL_TRUE;
   }

   if (format == GL_LUMINANCE_ALPHA && type == CHAN_TYPE && rbType == CHAN_TYPE) {
      const GLchan *src = (const GLchan *) pixels
         + (unpack.SkipRows * unpack.RowLength + unpack.SkipPixels)*2;
      if (simpleZoom) {
         GLint row;
         ASSERT(drawWidth <= MAX_WIDTH);
         for (row = 0; row < drawHeight; row++) {
            GLint i;
            const GLchan *ptr = src;
            for (i = 0;i<drawWidth;i++) {
               span.array->rgba[i][0] = *ptr;
               span.array->rgba[i][1] = *ptr;
               span.array->rgba[i][2] = *ptr++;
               span.array->rgba[i][3] = *ptr++;
            }
            rb->PutRow(ctx, rb, drawWidth, destX, destY,
                       span.array->rgba, NULL);
            src += unpack.RowLength*2;
            destY += yStep;
         }
      }
      else {
         /* with zooming */
         GLint row;
         ASSERT(drawWidth <= MAX_WIDTH);
         for (row = 0; row < drawHeight; row++) {
            const GLchan *ptr = src;
            GLint i;
            for (i = 0;i<drawWidth;i++) {
               span.array->rgba[i][0] = *ptr;
               span.array->rgba[i][1] = *ptr;
               span.array->rgba[i][2] = *ptr++;
               span.array->rgba[i][3] = *ptr++;
            }
            span.x = destX;
            span.y = destY;
            span.end = drawWidth;
            _swrast_write_zoomed_rgba_span(ctx, imgX, imgY, &span,
                                           span.array->rgba);
            src += unpack.RowLength*2;
            destY++;
         }
      }
      return GL_TRUE;
   }

   if (format == GL_COLOR_INDEX && type == GL_UNSIGNED_BYTE) {
      const GLubyte *src = (const GLubyte *) pixels
         + unpack.SkipRows * unpack.RowLength + unpack.SkipPixels;
      if (rbType == GL_UNSIGNED_BYTE) {
         /* convert ubyte/CI data to ubyte/RGBA */
         if (simpleZoom) {
            GLint row;
            for (row = 0; row < drawHeight; row++) {
               ASSERT(drawWidth <= MAX_WIDTH);
               _mesa_map_ci8_to_rgba8(ctx, drawWidth, src,
                                      span.array->rgba8);
               rb->PutRow(ctx, rb, drawWidth, destX, destY,
                          span.array->rgba8, NULL);
               src += unpack.RowLength;
               destY += yStep;
            }
         }
         else {
            /* ubyte/CI to ubyte/RGBA with zooming */
            GLint row;
            for (row = 0; row < drawHeight; row++) {
               ASSERT(drawWidth <= MAX_WIDTH);
               _mesa_map_ci8_to_rgba8(ctx, drawWidth, src,
                                      span.array->rgba8);
               span.x = destX;
               span.y = destY;
               span.end = drawWidth;
               _swrast_write_zoomed_rgba_span(ctx, imgX, imgY, &span,
                                              span.array->rgba8);
               src += unpack.RowLength;
               destY++;
            }
         }
         return GL_TRUE;
      }
   }

   /* can't handle this pixel format and/or data type */
   return GL_FALSE;
}
예제 #2
0
/*
 * Try to do a fast and simple RGB(a) glDrawPixels.
 * Return:  GL_TRUE if success, GL_FALSE if slow path must be used instead
 */
static GLboolean
fast_draw_pixels(GLcontext *ctx, GLint x, GLint y,
                 GLsizei width, GLsizei height,
                 GLenum format, GLenum type,
                 const struct gl_pixelstore_attrib *unpack,
                 const GLvoid *pixels)
{
   SWcontext *swrast = SWRAST_CONTEXT(ctx);
   struct sw_span span;

   INIT_SPAN(span, GL_BITMAP, 0, 0, SPAN_RGBA);

   if (!ctx->Current.RasterPosValid) {
      return GL_TRUE;      /* no-op */
   }

   if (ctx->Depth.Test)
      _swrast_span_default_z(ctx, &span);
   if (ctx->Fog.Enabled)
      _swrast_span_default_fog(ctx, &span);
   if (ctx->Texture._EnabledCoordUnits)
      _swrast_span_default_texcoords(ctx, &span);

   if ((SWRAST_CONTEXT(ctx)->_RasterMask & ~CLIP_BIT) == 0
       && ctx->Texture._EnabledCoordUnits == 0
       && unpack->Alignment == 1
       && !unpack->SwapBytes
       && !unpack->LsbFirst) {

      GLint destX = x;
      GLint destY = y;
      GLint drawWidth = width;           /* actual width drawn */
      GLint drawHeight = height;         /* actual height drawn */
      GLint skipPixels = unpack->SkipPixels;
      GLint skipRows = unpack->SkipRows;
      GLint rowLength;
      GLint zoomY0 = 0;

      if (unpack->RowLength > 0)
         rowLength = unpack->RowLength;
      else
         rowLength = width;

      /* If we're not using pixel zoom then do all clipping calculations
       * now.  Otherwise, we'll let the _swrast_write_zoomed_*_span() functions
       * handle the clipping.
       */
      if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
         /* horizontal clipping */
         if (destX < ctx->DrawBuffer->_Xmin) {
            skipPixels += (ctx->DrawBuffer->_Xmin - destX);
            drawWidth  -= (ctx->DrawBuffer->_Xmin - destX);
            destX = ctx->DrawBuffer->_Xmin;
         }
         if (destX + drawWidth > ctx->DrawBuffer->_Xmax)
            drawWidth -= (destX + drawWidth - ctx->DrawBuffer->_Xmax);
         if (drawWidth <= 0)
            return GL_TRUE;

         /* vertical clipping */
         if (destY < ctx->DrawBuffer->_Ymin) {
            skipRows   += (ctx->DrawBuffer->_Ymin - destY);
            drawHeight -= (ctx->DrawBuffer->_Ymin - destY);
            destY = ctx->DrawBuffer->_Ymin;
         }
         if (destY + drawHeight > ctx->DrawBuffer->_Ymax)
            drawHeight -= (destY + drawHeight - ctx->DrawBuffer->_Ymax);
         if (drawHeight <= 0)
            return GL_TRUE;
      }
      else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
         /* upside-down image */
         /* horizontal clipping */
         if (destX < ctx->DrawBuffer->_Xmin) {
            skipPixels += (ctx->DrawBuffer->_Xmin - destX);
            drawWidth  -= (ctx->DrawBuffer->_Xmin - destX);
            destX = ctx->DrawBuffer->_Xmin;
         }
         if (destX + drawWidth > ctx->DrawBuffer->_Xmax)
            drawWidth -= (destX + drawWidth - ctx->DrawBuffer->_Xmax);
         if (drawWidth <= 0)
            return GL_TRUE;

         /* vertical clipping */
         if (destY > ctx->DrawBuffer->_Ymax) {
            skipRows   += (destY - ctx->DrawBuffer->_Ymax);
            drawHeight -= (destY - ctx->DrawBuffer->_Ymax);
            destY = ctx->DrawBuffer->_Ymax;
         }
         if (destY - drawHeight < ctx->DrawBuffer->_Ymin)
            drawHeight -= (ctx->DrawBuffer->_Ymin - (destY - drawHeight));
         if (drawHeight <= 0)
            return GL_TRUE;
      }
      else {
         if (drawWidth > MAX_WIDTH)
            return GL_FALSE; /* fall back to general case path */

         /* save Y value of first row */
         zoomY0 = IROUND(ctx->Current.RasterPos[1]);
      }


      /*
       * Ready to draw!
       * The window region at (destX, destY) of size (drawWidth, drawHeight)
       * will be written to.
       * We'll take pixel data from buffer pointed to by "pixels" but we'll
       * skip "skipRows" rows and skip "skipPixels" pixels/row.
       */

      if (format == GL_RGBA && type == CHAN_TYPE
          && ctx->_ImageTransferState==0) {
         if (ctx->Visual.rgbMode) {
            GLchan *src = (GLchan *) pixels
               + (skipRows * rowLength + skipPixels) * 4;
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               /* no zooming */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                              (CONST GLchan (*)[4]) src, NULL);
                  src += rowLength * 4;
                  destY++;
               }
            }
            else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
               /* upside-down */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  destY--;
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                              (CONST GLchan (*)[4]) src, NULL);
                  src += rowLength * 4;
               }
            }
            else {
               /* with zooming */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  span.x = destX;
                  span.y = destY;
                  span.end = drawWidth;
                  _swrast_write_zoomed_rgba_span(ctx, &span,
                                        (CONST GLchan (*)[4]) src, zoomY0, 0);
                  src += rowLength * 4;
                  destY++;
               }
            }
         }
         return GL_TRUE;
      }
      else if (format == GL_RGB && type == CHAN_TYPE
               && ctx->_ImageTransferState == 0) {
         if (ctx->Visual.rgbMode) {
            GLchan *src = (GLchan *) pixels
               + (skipRows * rowLength + skipPixels) * 3;
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  (*swrast->Driver.WriteRGBSpan)(ctx, drawWidth, destX, destY,
                                              (CONST GLchan (*)[3]) src, NULL);
                  src += rowLength * 3;
                  destY++;
               }
            }
            else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
               /* upside-down */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  destY--;
                  (*swrast->Driver.WriteRGBSpan)(ctx, drawWidth, destX, destY,
                                              (CONST GLchan (*)[3]) src, NULL);
                  src += rowLength * 3;
               }
            }
            else {
               /* with zooming */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  span.x = destX;
                  span.y = destY;
                  span.end = drawWidth;
                  _swrast_write_zoomed_rgb_span(ctx, &span, 
                                         (CONST GLchan (*)[3]) src, zoomY0, 0);
                  src += rowLength * 3;
                  destY++;
               }
            }
         }
         return GL_TRUE;
      }
      else if (format == GL_LUMINANCE && type == CHAN_TYPE
               && ctx->_ImageTransferState==0) {
         if (ctx->Visual.rgbMode) {
            GLchan *src = (GLchan *) pixels
               + (skipRows * rowLength + skipPixels);
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               /* no zooming */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLint i;
		  for (i=0;i<drawWidth;i++) {
                     span.array->rgb[i][0] = src[i];
                     span.array->rgb[i][1] = src[i];
                     span.array->rgb[i][2] = src[i];
		  }
                  (*swrast->Driver.WriteRGBSpan)(ctx, drawWidth, destX, destY,
                                  (CONST GLchan (*)[3]) span.array->rgb, NULL);
                  src += rowLength;
                  destY++;
               }
            }
            else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
               /* upside-down */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLint i;
                  for (i=0;i<drawWidth;i++) {
                     span.array->rgb[i][0] = src[i];
                     span.array->rgb[i][1] = src[i];
                     span.array->rgb[i][2] = src[i];
                  }
                  destY--;
                  (*swrast->Driver.WriteRGBSpan)(ctx, drawWidth, destX, destY,
                                  (CONST GLchan (*)[3]) span.array->rgb, NULL);
                  src += rowLength;
               }
            }
            else {
               /* with zooming */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLint i;
		  for (i=0;i<drawWidth;i++) {
                     span.array->rgb[i][0] = src[i];
                     span.array->rgb[i][1] = src[i];
                     span.array->rgb[i][2] = src[i];
		  }
                  span.x = destX;
                  span.y = destY;
                  span.end = drawWidth;
                  _swrast_write_zoomed_rgb_span(ctx, &span,
                             (CONST GLchan (*)[3]) span.array->rgb, zoomY0, 0);
                  src += rowLength;
                  destY++;
               }
            }
         }
         return GL_TRUE;
      }
      else if (format == GL_LUMINANCE_ALPHA && type == CHAN_TYPE
               && ctx->_ImageTransferState == 0) {
         if (ctx->Visual.rgbMode) {
            GLchan *src = (GLchan *) pixels
               + (skipRows * rowLength + skipPixels)*2;
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               /* no zooming */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLint i;
                  GLchan *ptr = src;
		  for (i=0;i<drawWidth;i++) {
                     span.array->rgba[i][0] = *ptr;
                     span.array->rgba[i][1] = *ptr;
                     span.array->rgba[i][2] = *ptr++;
                     span.array->rgba[i][3] = *ptr++;
		  }
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                 (CONST GLchan (*)[4]) span.array->rgba, NULL);
                  src += rowLength*2;
                  destY++;
               }
            }
            else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
               /* upside-down */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLint i;
                  GLchan *ptr = src;
                  for (i=0;i<drawWidth;i++) {
                     span.array->rgba[i][0] = *ptr;
                     span.array->rgba[i][1] = *ptr;
                     span.array->rgba[i][2] = *ptr++;
                     span.array->rgba[i][3] = *ptr++;
                  }
                  destY--;
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                 (CONST GLchan (*)[4]) span.array->rgba, NULL);
                  src += rowLength*2;
               }
            }
            else {
               /* with zooming */
               GLint row;
               ASSERT(drawWidth <= MAX_WIDTH);
               for (row=0; row<drawHeight; row++) {
                  GLchan *ptr = src;
                  GLint i;
		  for (i=0;i<drawWidth;i++) {
                     span.array->rgba[i][0] = *ptr;
                     span.array->rgba[i][1] = *ptr;
                     span.array->rgba[i][2] = *ptr++;
                     span.array->rgba[i][3] = *ptr++;
		  }
                  span.x = destX;
                  span.y = destY;
                  span.end = drawWidth;
                  _swrast_write_zoomed_rgba_span(ctx, &span,
                            (CONST GLchan (*)[4]) span.array->rgba, zoomY0, 0);
                  src += rowLength*2;
                  destY++;
               }
            }
         }
         return GL_TRUE;
      }
      else if (format==GL_COLOR_INDEX && type==GL_UNSIGNED_BYTE) {
         GLubyte *src = (GLubyte *) pixels + skipRows * rowLength + skipPixels;
         if (ctx->Visual.rgbMode) {
            /* convert CI data to RGBA */
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               /* no zooming */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  ASSERT(drawWidth <= MAX_WIDTH);
                  _mesa_map_ci8_to_rgba(ctx, drawWidth, src, span.array->rgba);
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                 (const GLchan (*)[4]) span.array->rgba, NULL);
                  src += rowLength;
                  destY++;
               }
               return GL_TRUE;
            }
            else if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==-1.0F) {
               /* upside-down */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  ASSERT(drawWidth <= MAX_WIDTH);
                  _mesa_map_ci8_to_rgba(ctx, drawWidth, src, span.array->rgba);
                  destY--;
                  (*swrast->Driver.WriteRGBASpan)(ctx, drawWidth, destX, destY,
                                 (CONST GLchan (*)[4]) span.array->rgba, NULL);
                  src += rowLength;
               }
               return GL_TRUE;
            }
            else {
               /* with zooming */
               GLint row;
               for (row=0; row<drawHeight; row++) {
                  ASSERT(drawWidth <= MAX_WIDTH);
                  _mesa_map_ci8_to_rgba(ctx, drawWidth, src, span.array->rgba);
                  span.x = destX;
                  span.y = destY;
                  span.end = drawWidth;
                  _swrast_write_zoomed_rgba_span(ctx, &span,
                            (CONST GLchan (*)[4]) span.array->rgba, zoomY0, 0);
                  src += rowLength;
                  destY++;
               }
               return GL_TRUE;
            }
         }
         else if (ctx->_ImageTransferState==0) {
            /* write CI data to CI frame buffer */
            GLint row;
            if (ctx->Pixel.ZoomX==1.0F && ctx->Pixel.ZoomY==1.0F) {
               /* no zooming */
               for (row=0; row<drawHeight; row++) {
                  (*swrast->Driver.WriteCI8Span)(ctx, drawWidth, destX, destY,
                                              src, NULL);
                  src += rowLength;
                  destY++;
               }
               return GL_TRUE;
            }
            else {
               /* with zooming */
               return GL_FALSE;
            }
         }
      }
      else {
         /* can't handle this pixel format and/or data type here */
         return GL_FALSE;
      }
   }

   /* can't do a simple draw, have to use slow path */
   return GL_FALSE;
}