s_span.c

Mesa is an open-source implementation of the OpenGL specification - a system for rendering interacti

/**
 * Compute mipmap LOD from partial derivatives.
 * This the ideal solution, as given in the OpenGL spec.
 */
#if 0
static GLfloat
compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
               GLfloat dqdx, GLfloat dqdy, GLfloat texW, GLfloat texH,
               GLfloat s, GLfloat t, GLfloat q, GLfloat invQ)
{
   GLfloat dudx = texW * ((s + dsdx) / (q + dqdx) - s * invQ);
   GLfloat dvdx = texH * ((t + dtdx) / (q + dqdx) - t * invQ);
   GLfloat dudy = texW * ((s + dsdy) / (q + dqdy) - s * invQ);
   GLfloat dvdy = texH * ((t + dtdy) / (q + dqdy) - t * invQ);
   GLfloat x = SQRTF(dudx * dudx + dvdx * dvdx);
   GLfloat y = SQRTF(dudy * dudy + dvdy * dvdy);
   GLfloat rho = MAX2(x, y);
   GLfloat lambda = LOG2(rho);
   return lambda;
}
#endif


/**
 * Compute mipmap LOD from partial derivatives.
 * This is a faster approximation than above function.
 */
GLfloat
_swrast_compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
                     GLfloat dqdx, GLfloat dqdy, GLfloat texW, GLfloat texH,
                     GLfloat s, GLfloat t, GLfloat q, GLfloat invQ)
{
   GLfloat dsdx2 = (s + dsdx) / (q + dqdx) - s * invQ;
   GLfloat dtdx2 = (t + dtdx) / (q + dqdx) - t * invQ;
   GLfloat dsdy2 = (s + dsdy) / (q + dqdy) - s * invQ;
   GLfloat dtdy2 = (t + dtdy) / (q + dqdy) - t * invQ;
   GLfloat maxU, maxV, rho, lambda;
   dsdx2 = FABSF(dsdx2);
   dsdy2 = FABSF(dsdy2);
   dtdx2 = FABSF(dtdx2);
   dtdy2 = FABSF(dtdy2);
   maxU = MAX2(dsdx2, dsdy2) * texW;
   maxV = MAX2(dtdx2, dtdy2) * texH;
   rho = MAX2(maxU, maxV);
   lambda = LOG2(rho);
   return lambda;
}


/**
 * Fill in the span.array->attrib[FRAG_ATTRIB_TEXn] arrays from the
 * using the attrStart/Step values.
 *
 * This function only used during fixed-function fragment processing.
 *
 * Note: in the places where we divide by Q (or mult by invQ) we're
 * really doing two things: perspective correction and texcoord
 * projection.  Remember, for texcoord (s,t,r,q) we need to index
 * texels with (s/q, t/q, r/q).
 */
static void
interpolate_texcoords(GLcontext *ctx, SWspan *span)
{
   const GLuint maxUnit
      = (ctx->Texture._EnabledCoordUnits > 1) ? ctx->Const.MaxTextureUnits : 1;
   GLuint u;

   /* XXX CoordUnits vs. ImageUnits */
   for (u = 0; u < maxUnit; u++) {
      if (ctx->Texture._EnabledCoordUnits & (1 << u)) {
         const GLuint attr = FRAG_ATTRIB_TEX0 + u;
         const struct gl_texture_object *obj = ctx->Texture.Unit[u]._Current;
         GLfloat texW, texH;
         GLboolean needLambda;
         GLfloat (*texcoord)[4] = span->array->attribs[attr];
         GLfloat *lambda = span->array->lambda[u];
         const GLfloat dsdx = span->attrStepX[attr][0];
         const GLfloat dsdy = span->attrStepY[attr][0];
         const GLfloat dtdx = span->attrStepX[attr][1];
         const GLfloat dtdy = span->attrStepY[attr][1];
         const GLfloat drdx = span->attrStepX[attr][2];
         const GLfloat dqdx = span->attrStepX[attr][3];
         const GLfloat dqdy = span->attrStepY[attr][3];
         GLfloat s = span->attrStart[attr][0];
         GLfloat t = span->attrStart[attr][1];
         GLfloat r = span->attrStart[attr][2];
         GLfloat q = span->attrStart[attr][3];

         if (obj) {
            const struct gl_texture_image *img = obj->Image[0][obj->BaseLevel];
            needLambda = (obj->MinFilter != obj->MagFilter)
               || ctx->FragmentProgram._Current;
            texW = img->WidthScale;
            texH = img->HeightScale;
         }
         else {
            /* using a fragment program */
            texW = 1.0;
            texH = 1.0;
            needLambda = GL_FALSE;
         }

         if (needLambda) {
            GLuint i;
            if (ctx->FragmentProgram._Current
                || ctx->ATIFragmentShader._Enabled) {
               /* do perspective correction but don't divide s, t, r by q */
               const GLfloat dwdx = span->attrStepX[FRAG_ATTRIB_WPOS][3];
               GLfloat w = span->attrStart[FRAG_ATTRIB_WPOS][3];
               for (i = 0; i < span->end; i++) {
                  const GLfloat invW = 1.0F / w;
                  texcoord[i][0] = s * invW;
                  texcoord[i][1] = t * invW;
                  texcoord[i][2] = r * invW;
                  texcoord[i][3] = q * invW;
                  lambda[i] = _swrast_compute_lambda(dsdx, dsdy, dtdx, dtdy,
                                                     dqdx, dqdy, texW, texH,
                                                     s, t, q, invW);
                  s += dsdx;
                  t += dtdx;
                  r += drdx;
                  q += dqdx;
                  w += dwdx;
               }
            }
            else {
               for (i = 0; i < span->end; i++) {
                  const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
                  texcoord[i][0] = s * invQ;
                  texcoord[i][1] = t * invQ;
                  texcoord[i][2] = r * invQ;
                  texcoord[i][3] = q;
                  lambda[i] = _swrast_compute_lambda(dsdx, dsdy, dtdx, dtdy,
                                                     dqdx, dqdy, texW, texH,
                                                     s, t, q, invQ);
                  s += dsdx;
                  t += dtdx;
                  r += drdx;
                  q += dqdx;
               }
            }
            span->arrayMask |= SPAN_LAMBDA;
         }
         else {
            GLuint i;
            if (ctx->FragmentProgram._Current ||
                ctx->ATIFragmentShader._Enabled) {
               /* do perspective correction but don't divide s, t, r by q */
               const GLfloat dwdx = span->attrStepX[FRAG_ATTRIB_WPOS][3];
               GLfloat w = span->attrStart[FRAG_ATTRIB_WPOS][3];
               for (i = 0; i < span->end; i++) {
                  const GLfloat invW = 1.0F / w;
                  texcoord[i][0] = s * invW;
                  texcoord[i][1] = t * invW;
                  texcoord[i][2] = r * invW;
                  texcoord[i][3] = q * invW;
                  lambda[i] = 0.0;
                  s += dsdx;
                  t += dtdx;
                  r += drdx;
                  q += dqdx;
                  w += dwdx;
               }
            }
            else if (dqdx == 0.0F) {
               /* Ortho projection or polygon's parallel to window X axis */
               const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
               for (i = 0; i < span->end; i++) {
                  texcoord[i][0] = s * invQ;
                  texcoord[i][1] = t * invQ;
                  texcoord[i][2] = r * invQ;
                  texcoord[i][3] = q;
                  lambda[i] = 0.0;
                  s += dsdx;
                  t += dtdx;
                  r += drdx;
               }
            }
            else {
               for (i = 0; i < span->end; i++) {
                  const GLfloat invQ = (q == 0.0F) ? 1.0F : (1.0F / q);
                  texcoord[i][0] = s * invQ;
                  texcoord[i][1] = t * invQ;
                  texcoord[i][2] = r * invQ;
                  texcoord[i][3] = q;
                  lambda[i] = 0.0;
                  s += dsdx;
                  t += dtdx;
                  r += drdx;
                  q += dqdx;
               }
            }
         } /* lambda */
      } /* if */
   } /* for */
}


/**
 * Fill in the arrays->attribs[FRAG_ATTRIB_WPOS] array.
 */
static INLINE void
interpolate_wpos(GLcontext *ctx, SWspan *span)
{
   GLfloat (*wpos)[4] = span->array->attribs[FRAG_ATTRIB_WPOS];
   GLuint i;
   const GLfloat zScale = 1.0 / ctx->DrawBuffer->_DepthMaxF;
   GLfloat w, dw;

   if (span->arrayMask & SPAN_XY) {
      for (i = 0; i < span->end; i++) {
         wpos[i][0] = (GLfloat) span->array->x[i];
         wpos[i][1] = (GLfloat) span->array->y[i];
      }
   }
   else {
      for (i = 0; i < span->end; i++) {
         wpos[i][0] = (GLfloat) span->x + i;
         wpos[i][1] = (GLfloat) span->y;
      }
   }

   w = span->attrStart[FRAG_ATTRIB_WPOS][3];
   dw = span->attrStepX[FRAG_ATTRIB_WPOS][3];
   for (i = 0; i < span->end; i++) {
      wpos[i][2] = (GLfloat) span->array->z[i] * zScale;
      wpos[i][3] = w;
      w += dw;
   }
}


/**
 * Apply the current polygon stipple pattern to a span of pixels.
 */
static INLINE void
stipple_polygon_span(GLcontext *ctx, SWspan *span)
{
   GLubyte *mask = span->array->mask;

   ASSERT(ctx->Polygon.StippleFlag);

   if (span->arrayMask & SPAN_XY) {
      /* arrays of x/y pixel coords */
      GLuint i;
      for (i = 0; i < span->end; i++) {
         const GLint col = span->array->x[i] % 32;
         const GLint row = span->array->y[i] % 32;
         const GLuint stipple = ctx->PolygonStipple[row];
         if (((1 << col) & stipple) == 0) {
            mask[i] = 0;
         }
      }
   }
   else {
      /* horizontal span of pixels */
      const GLuint highBit = 1 << 31;
      const GLuint stipple = ctx->PolygonStipple[span->y % 32];
      GLuint i, m = highBit >> (GLuint) (span->x % 32);
      for (i = 0; i < span->end; i++) {
         if ((m & stipple) == 0) {
            mask[i] = 0;
         }
         m = m >> 1;
         if (m == 0) {
            m = highBit;
         }
      }
   }
   span->writeAll = GL_FALSE;
}


/**
 * Clip a pixel span to the current buffer/window boundaries:
 * DrawBuffer->_Xmin, _Xmax, _Ymin, _Ymax.  This will accomplish
 * window clipping and scissoring.
 * Return:   GL_TRUE   some pixels still visible
 *           GL_FALSE  nothing visible
 */
static INLINE GLuint
clip_span( GLcontext *ctx, SWspan *span )
{
   const GLint xmin = ctx->DrawBuffer->_Xmin;
   const GLint xmax = ctx->DrawBuffer->_Xmax;
   const GLint ymin = ctx->DrawBuffer->_Ymin;
   const GLint ymax = ctx->DrawBuffer->_Ymax;

   if (span->arrayMask & SPAN_XY) {
      /* arrays of x/y pixel coords */
      const GLint *x = span->array->x;
      const GLint *y = span->array->y;
      const GLint n = span->end;
      GLubyte *mask = span->array->mask;
      GLint i;
      if (span->arrayMask & SPAN_MASK) {
         /* note: using & intead of && to reduce branches */
         for (i = 0; i < n; i++) {
            mask[i] &= (x[i] >= xmin) & (x[i] < xmax)
                     & (y[i] >= ymin) & (y[i] < ymax);
         }
      }
      else {
         /* note: using & intead of && to reduce branches */
         for (i = 0; i < n; i++) {
            mask[i] = (x[i] >= xmin) & (x[i] < xmax)
                    & (y[i] >= ymin) & (y[i] < ymax);
         }
      }
      return GL_TRUE;  /* some pixels visible */
   }
   else {
      /* horizontal span of pixels */
      const GLint x = span->x;
      const GLint y = span->y;
      const GLint n = span->end;

      /* Trivial rejection tests */
      if (y < ymin || y >= ymax || x + n <= xmin || x >= xmax) {
         span->end = 0;
         return GL_FALSE;  /* all pixels clipped */
      }

      /* Clip to the left */
      if (x < xmin) {
         ASSERT(x + n > xmin);
         span->writeAll = GL_FALSE;
         _mesa_bzero(span->array->mask, (xmin - x) * sizeof(GLubyte));
      }

      /* Clip to right */
      if (x + n > xmax) {
         ASSERT(x < xmax);
         span->end = xmax - x;
      }

      return GL_TRUE;  /* some pixels visible */
   }
}


/**
 * Apply all the per-fragment opertions to a span of color index fragments
 * and write them to the enabled color drawbuffers.
 * The 'span' parameter can be considered to be const.  Note that
 * span->interpMask and span->arrayMask may be changed but will be restored
 * to their original values before returning.
 */
void
_swrast_write_index_span( GLcontext *ctx, SWspan *span)
{
   const SWcontext *swrast = SWRAST_CONTEXT(ctx);
   const GLbitfield origInterpMask = span->interpMask;
   const GLbitfield origArrayMask = span->arrayMask;
   struct gl_framebuffer *fb = ctx->DrawBuffer;

   ASSERT(span->end <= MAX_WIDTH);
   ASSERT(span->primitive == GL_POINT  ||  span->primitive == GL_LINE ||
	  span->primitive == GL_POLYGON  ||  span->primitive == GL_BITMAP);
   ASSERT((span->interpMask | span->arrayMask) & SPAN_INDEX);
   /*
   ASSERT((span->interpMask & span->arrayMask) == 0);
   */

   if (span->arrayMask & SPAN_MASK) {
      /* mask was initialized by caller, probably glBitmap */
      span->writeAll = GL_FALSE;
   }
   else {
      _mesa_memset(span->array->mask, 1, span->end);
      span->writeAll = GL_TRUE;
   }

   /* Clipping */
   if ((swrast->_RasterMask & CLIP_BIT) || (span->primitive != GL_POLYGON)) {
      if (!clip_span(ctx, span)) {
         return;
      }
   }

   /* Depth bounds test */
   if (ctx->Depth.BoundsTest && fb->Visual.depthBits > 0) {
      if (!_swrast_depth_bounds_test(ctx, span)) {
         return;
      }
   }

#ifdef DEBUG
   /* Make sure all fragments are within window bounds */
   if (span->arrayMask & SPAN_XY) {
      GLuint i;
      for (i = 0; i < span->end; i++) {
         if (span->array->mask[i]) {
            assert(span->array->x[i] >= fb->_Xmin);
            assert(span->array->x[i] < fb->_Xmax);
            assert(span->array->y[i] >= fb->_Ymin);
            assert(span->array->y[i] < fb->_Ymax);
         }
      }
   }
#endif

   /* Polygon Stippling */
   if (ctx->Polygon.StippleFlag && span->primitive == GL_POLYGON) {
      stipple_polygon_span(ctx, span);
   }

   /* Stencil and Z testing */
   if (ctx->Depth.Test || ctx->Stencil.Enabled) {
      if (!(span->arrayMask & SPAN_Z))
         _swrast_span_interpolate_z(ctx, span);

      if (ctx->Stencil.Enabled) {
         if (!_swrast_stencil_and_ztest_span(ctx, span)) {
            span->arrayMask = origArrayMask;
            return;
         }
      }
      else {
         ASSERT(ctx->Depth.Test);
         if (!_swrast_depth_test_span(ctx, span)) {
            span->interpMask = origInterpMask;
            span->arrayMask = origArrayMask;
            return;
         }
      }
   }

#if FEATURE_ARB_occlusion_query
   if (ctx->Query.CurrentOcclusionObject) {
      /* update count of 'passed' fragments */
      struct gl_query_object *q = ctx->Query.CurrentOcclusionObject;
      GLuint i;
      for (i = 0; i < span->end; i++)
         q->Result += span->array->mask[i];
   }