?? circle.c
字號:
// Since the error term is non-negative, adjust it based on a move
// in both the A and B deltas.
//
lD += (4 * (lA - lB)) + 10;
//
// Decrement the B delta.
//
lB -= 1;
}
//
// Increment the A delta.
//
lA++;
}
}
//*****************************************************************************
//
//! Draws a filled circle.
//!
//! \param pContext is a pointer to the drawing context to use.
//! \param lX is the X coordinate of the center of the circle.
//! \param lY is the Y coordinate of the center of the circle.
//! \param lRadius is the radius of the circle.
//!
//! This function draws a filled circle, utilizing the Bresenham circle drawing
//! algorithm. The extent of the circle is from \e lX - \e lRadius to \e lX +
//! \e lRadius and \e lY - \e lRadius to \e lY + \e lRadius, inclusive.
//!
//! \return None.
//
//*****************************************************************************
void
GrCircleFill(const tContext *pContext, long lX, long lY, long lRadius)
{
long lA, lB, lD, lX1, lX2, lY1;
//
// Check the arguments.
//
ASSERT(pContext);
//
// Initialize the variables that control the Bresenham circle drawing
// algorithm.
//
lA = 0;
lB = lRadius;
lD = 3 - (2 * lRadius);
//
// Loop until the A delta is greater than the B delta, meaning that the
// entire circle has been filled.
//
while(lA <= lB)
{
//
// Determine the row when subtracting the A delta.
//
lY1 = lY - lA;
//
// See if this row is within the clipping region.
//
if((lY1 >= pContext->sClipRegion.sYMin) &&
(lY1 <= pContext->sClipRegion.sYMax))
{
//
// Determine the column when subtracting the B delta, and move it
// to the left edge of the clipping region if it is to the left of
// the clipping region.
//
lX1 = lX - lB;
if(lX1 < pContext->sClipRegion.sXMin)
{
lX1 = pContext->sClipRegion.sXMin;
}
//
// Determine the column when adding the B delta, and move it to the
// right edge of the clipping region if it is to the right of the
// clipping region.
//
lX2 = lX + lB;
if(lX2 > pContext->sClipRegion.sXMax)
{
lX2 = pContext->sClipRegion.sXMax;
}
//
// Draw a horizontal line if this portion of the circle is within
// the clipping region.
//
if(lX1 <= lX2)
{
GrLineDrawH(pContext, lX1, lX2, lY1);
}
}
//
// Determine the row when adding the A delta.
//
lY1 = lY + lA;
//
// See if this row is within the clipping region, and the A delta is
// not zero (otherwise, this describes the same row of the circle).
//
if((lY1 >= pContext->sClipRegion.sYMin) &&
(lY1 <= pContext->sClipRegion.sYMax) &&
(lA != 0))
{
//
// Determine the column when subtracting the B delta, and move it
// to the left edge of the clipping region if it is to the left of
// the clipping region.
//
lX1 = lX - lB;
if(lX1 < pContext->sClipRegion.sXMin)
{
lX1 = pContext->sClipRegion.sXMin;
}
//
// Determine the column when adding the B delta, and move it to the
// right edge of the clipping region if it is to the right of the
// clipping region.
//
lX2 = lX + lB;
if(lX2 > pContext->sClipRegion.sXMax)
{
lX2 = pContext->sClipRegion.sXMax;
}
//
// Draw a horizontal line if this portion of the circle is within
// the clipping region.
//
if(lX1 <= lX2)
{
GrLineDrawH(pContext, lX1, lX2, lY1);
}
}
//
// Only draw the complementary lines if the B delta is about to change
// and the A and B delta are different (otherwise, they describe the
// same set of pixels).
//
if((lD >= 0) && (lA != lB))
{
//
// Determine the row when subtracting the B delta.
//
lY1 = lY - lB;
//
// See if this row is within the clipping region.
//
if((lY1 >= pContext->sClipRegion.sYMin) &&
(lY1 <= pContext->sClipRegion.sYMax))
{
//
// Determine the column when subtracting the A delta, and move
// it to the left edge of the clipping regino if it is to the
// left of the clipping region.
//
lX1 = lX - lA;
if(lX1 < pContext->sClipRegion.sXMin)
{
lX1 = pContext->sClipRegion.sXMin;
}
//
// Determine the column when adding the A delta, and move it to
// the right edge of the clipping region if it is to the right
// of the clipping region.
//
lX2 = lX + lA;
if(lX2 > pContext->sClipRegion.sXMax)
{
lX2 = pContext->sClipRegion.sXMax;
}
//
// Draw a horizontal line if this portion of the circle is
// within the clipping region.
//
if(lX1 <= lX2)
{
GrLineDrawH(pContext, lX1, lX2, lY1);
}
}
//
// Determine the row when adding the B delta.
//
lY1 = lY + lB;
//
// See if this row is within the clipping region.
//
if((lY1 >= pContext->sClipRegion.sYMin) &&
(lY1 <= pContext->sClipRegion.sYMax))
{
//
// Determine the column when subtracting the A delta, and move
// it to the left edge of the clipping region if it is to the
// left of the clipping region.
//
lX1 = lX - lA;
if(lX1 < pContext->sClipRegion.sXMin)
{
lX1 = pContext->sClipRegion.sXMin;
}
//
// Determine the column when adding the A delta, and move it to
// the right edge of the clipping region if it is to the right
// of the clipping region.
//
lX2 = lX + lA;
if(lX2 > pContext->sClipRegion.sXMax)
{
lX2 = pContext->sClipRegion.sXMax;
}
//
// Draw a horizontal line if this portion of the circle is
// within the clipping region.
//
if(lX1 <= lX2)
{
GrLineDrawH(pContext, lX1, lX2, lY1);
}
}
}
//
// See if the error term is negative.
//
if(lD < 0)
{
//
// Since the error term is negative, adjust it based on a move in
// only the A delta.
//
lD += (4 * lA) + 6;
}
else
{
//
// Since the error term is non-negative, adjust it based on a move
// in both the A and B deltas.
//
lD += (4 * (lA - lB)) + 10;
//
// Decrement the B delta.
//
lB -= 1;
}
//
// Increment the A delta.
//
lA++;
}
}
//*****************************************************************************
//
// Close the Doxygen group.
//! @}
//
//*****************************************************************************
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