US 7,064,771 B1Granted

Method and apparatus for compositing colors of images using pixel fragments with Z and Z gradient parameters

AssigneeCompaq Information Technologies Group, L.P.

InventorsNorman P. Jouppi, Chun-Fa Chang

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Abstract

A graphics data processing apparatus includes a graphics memory having pixel storage for storing up to a predetermined number of fragment values for the pixel. Each stored fragment value is associated with a fragment of an image that is visible in that pixel. When a new fragment is determined to be visible in the pixel, but all the available fragment values for the pixel are already in use, one of the previously stored fragment values is either replaced by, or combined with the fragment value for the new fragment. The resulting new fragment value is used to determine the color of the pixel. Alternately, if the new fragment is determined to be totally occluded by one or more of the other fragments, the new fragment may be discarded. Z-depth and Z gradient information is stored each fragment. This Z information is used to determine the relative depth values of the fragments, which in turn is used to determine which fragment to discard or to combine with another fragment when all the available fragment values for a pixel are already in use.

Claims20

Dependent claims

Image processing apparatus, comprising:

pixel memory storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
a pipeline processing circuit for processing a new fragment tuple representing a fragment added to the pixel, the pipeline processing circuit including a sequence of pipeline stage circuits, the pipeline stage circuits including:
a fragment ordering pipeline stage for ordering the new fragment tuple and the fragment tuples stored in the pixel memory so as to generate a sequence of fragment tuples ordered with respect to Z value;
a subpixel ordering pipeline stage for determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
subpixel Z value generation circuitry for determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
subpixel Z value comparison circuitry for comparing the determined Z values and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions;
and
a merge pipeline stage that uses the swap values to produce a modified sequence of fragment tuples, the merge pipeline stage merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, the merge pipeline including subpixel merge circuitry for merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values.

7 more elements

A method of rendering an image, comprising:

for each pixel of the image, storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
processing a new fragment tuple representing a fragment added to the pixel, including:
ordering the new fragment tuple and the fragment tuples stored for the pixel so as to generate a sequence of fragment tuples ordered with respect to Z value;
determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
comparing the determined Z values, and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions, the swap values being used to produce a modified sequence of fragment tuples;
and
merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, including merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values.

7 more elements

Image processing apparatus, comprising:

pixel memory storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
a pipeline processing circuit for processing a new fragment tuple representing a fragment added to the pixel, the pipeline processing circuit including a sequence of pipeline stage circuits, the pipeline stage circuits including:
a fragment ordering pipeline stage for ordering the new fragment tuple and the fragment tuples stored in the pixel memory so as to generate a sequence of fragment tuples ordered with respect to Z value;
a subpixel ordering pipeline stage for determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
subpixel Z value generation circuitry for determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
subpixel Z value comparison circuitry for comparing the determined Z values and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions, the swap values being used to produce a modified sequence of fragment tuples;
and
a merge pipeline stage merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, the merge pipeline including subpixel merge circuitry for merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values,
the merge pipeline stage including a Z difference circuit for determining a Z difference value for each pair of neighboring fragment tuples in the modified sequence of fragment tuples, a selection circuit for selecting two successive fragment tuples in the modified sequence of fragment tuples based on the Z difference values generated by the Z difference circuit, and a fragment merge circuit for merging the two selected fragment tuples to generate the merged fragment tuple,
wherein the fragment merge circuit generates a merged color value and merged transparency value for each of a plurality of subpixel sample positions within the pixel, and then combines the generated merged color values to generate a color value for the merged fragment tuple and combines the generated merged transparency values to generate a transparency value for the merged fragment tuple, and
wherein the fragment merge circuit further generates a Z value for the merged fragment tuple by averaging weighted Z values, the weighted Z values corresponding to the Z value of each of the neighboring fragment tuples multiplied by a number of subpixel sample positions covered by the corresponding fragment.

10 more elements

Image processing apparatus, comprising:

pixel memory storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
a pipeline processing circuit for processing a new fragment tuple representing a fragment added to the pixel, the pipeline processing circuit including a sequence of pipeline stage circuits, the pipeline stage circuits including:
a fragment ordering pipeline stage for ordering the new fragment tuple and the fragment tuples stored in the pixel memory so as to generate a sequence of fragment tuples ordered with respect to Z value;
a subpixel ordering pipeline stage for determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
subpixel Z value generation circuitry for determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
subpixel Z value comparison circuitry for comparing the determined Z values and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions, the swap values being used to produce a modified sequence of fragment tuples;
and
a merge pipeline stage merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, the merge pipeline including subpixel merge circuitry for merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values,
the merge pipeline stage including a Z difference circuit for determining a Z difference value for each pair of neighboring fragment tuples in the modified sequence of fragment tuples, a selection circuit for selecting two successive fragment tuples in the modified sequence of fragment tuples based on the Z difference values generated by the Z difference circuit, and a fragment merge circuit for merging the two selected fragment tuples to generate the merged fragment tuple, the two selected fragment tuples merged having associated therewith first Zdx and first Zdy gradient values and second Zdx and second Zdy gradient values,
wherein the fragment merge circuit generates a merged color value and merged transparency value for each of a plurality of subpixel sample positions within the pixel, and then combines the generated merged color values to generate a color value for the merged fragment tuple and combines the generated merged transparency values to generate a transparency value for the merged fragment tuple, and
wherein the fragment merge circuit further generates a pair of Z gradient values for the merged fragment tuple by comparing absolute values of the first and second Zdx gradient values and selecting one of the first and second Zdx gradient values in accordance with the result of the comparison thereof, and by comparing absolute values of the first and second Zdy gradient values and selecting one of the first and second Zdy gradient values in accordance with the result of the comparison thereof.

10 more elements

A method of rendering an image, comprising:

for each pixel of the image, storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
processing a new fragment tuple representing a fragment added to the pixel, including:
ordering the new fragment tuple and the fragment tuples stored for the pixel so as to generate a sequence of fragment tuples ordered with respect to Z value;
determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
comparing the determined Z values, and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions, the swap values being used to produce a modified sequence of fragment tuples;
and
merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, including merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values,
the merging step comprising determining a Z difference value for each pair of neighboring fragment tuples in the modified sequence of fragment tuples, selecting two successive fragment tuples in the modified sequence of fragment tuples based on the Z difference values, and merging the two selected fragment tuples to generate the merged fragment tuple,
the merging step further comprising generating a merged color value and merged transparency value for each of a plurality of subpixel sample positions within the pixel, combining the generated merged color values to generate a color value for the merged fragment tuple, and combining the generated merged transparency values to generate a transparency value for the merged fragment tuple,
the merging step additionally comprising generating a Z value for the merged fragment tuple by averaging weighted Z values, the weighted Z values corresponding to the Z value of each of the neighboring fragment tuples multiplied by a number of subpixel sample positions covered by the corresponding fragment.

10 more elements

A method of rendering an image, comprising:

for each pixel of the image, storing up to a predetermined number of fragment tuples, each stored fragment tuple being associated with a fragment that is visible in the pixel;
each fragment tuple including a color value, a center Z (depth) value, and a pair of Z gradient values;
processing a new fragment tuple representing a fragment added to the pixel, including:
ordering the new fragment tuple and the fragment tuples stored for the pixel so as to generate a sequence of fragment tuples ordered with respect to Z value;
determining if successive fragments in the sequence of fragments are out of order with respect to Z value at any of a predefined set of subpixel positions, including:
determining a Z value for two successive fragments tuples in the sequence of fragment tuples at each subpixel sample position, if any, covered by both of the two fragments represented by the two fragment tuples, based on the center Z value and pair of Z gradient values for each of the two fragments tuples;
and
comparing the determined Z values, and generating swap values indicating whether the fragments are out of order with respect to Z value at each of the predefined subpixel sample positions, the swap values being used to produce a modified sequence of fragment tuples;
and
merging two of the fragment tuples in the modified sequence of fragment tuples, when the sequence of fragment tuples includes more fragment tuples than said predetermined number, so as to generate a merged fragment tuple, including merging color values for the two fragment tuples at each of the predefined subpixel sample positions, if any, that is covered by both of the two fragments represented by the two fragment tuples being merged, the color values being merged at each such subpixel sample position in an order specified by a corresponding one of the swap values,
the merging step comprising determining a Z difference value for each pair of neighboring fragment tuples in the modified sequence of fragment tuples, selecting two successive fragment tuples in the modified sequence of fragment tuples based on the Z difference values, and merging the two selected fragment tuples to generate the merged fragment tuple, the two selected fragment tuples merged having associated therewith first Zdx and first Zdy gradient values and second Zdx and second Zdy gradient values,
the merging step further comprising generating a merged color value and merged transparency value for each of a plurality of subpixel sample positions within the pixel, combining the generated merged color values to generate a color value for the merged fragment tuple, and combining the generated merged transparency values to generate a transparency value for the merged fragment tuple,
the merging step additionally comprising generating a pair of Z gradient values for the merged fragment tuple by comparing absolute values of the first and second Zdx gradient values and selecting one of the first and second Zdx gradient values in accordance with the result of the comparison thereof, and by comparing absolute values of the first and second Zdy gradient values and selecting one of the first and second Zdy gradient values in accordance with the result of the comparison thereof.

10 more elements

Dependencies are inferred from the claim text.