Depth based blending for 3D graphics systems

• US 20030122823A1
• Filed: 02/14/2003
• Published: 07/03/2003
• Est. Priority Date: 09/17/1999
• Status: Active Grant

• Current Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Original Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Inventors: Howson, John William
• Granted Patent: US 6,809,730 B2
• Time in Patent Office: Days
• US Class Current: 345/426
• CPC Class Codes: G06T 15/06 Ray-tracing
• CPC Class Codes: G06T 15/40 Hidden part removal
• CPC Class Codes: G06T 15/405 using Z-buffer
• CPC Class Codes: G06T 15/50 Lighting effects
• CPC Class Codes: G06T 15/80 Shading
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 5/14 Display of multiple viewports

Abstract

Three dimensional computer graphic images are shaded by first supplying data which defines the objects to be inserted into the image, this data including depth data relating to the objects. A depth store (4) includes data for objects already inserted into the image and a depth comparison unit (6) compares the depth of an object to be inserted with the currently stored depth data for a particular pixel. The result of this is used to determine which of a number of depth operations is to be applied to the depth store (4). A blending value is selected for each pixel for combining the object with the image in dependence on the selected depth operation. A combining unit then combines the object with the image in proportions dependent upon the selecting blending value.

Claims

1. An apparatus for shading a three dimensional computer graphic image comprising

a) means for supplying data defining objects to be inserted into the image, the data including depth data relating to the object;

b) means for storing depth data for objects already inserted into the image;

c) means for comparing the depth of an object to be inserted with currently stored depth data for a pixel, at each pixel covered by the object to be inserted into the image;

d) means for selecting a depth operation to be applied to the means for storing depth data in dependence on the result of the comparison;

e) means for selecting a blending value, for each pixel for combining the object with the image, in dependence on the selected depth operation;

f) means for combining the object with the image in proportions dependent upon the selected blending value;

g) means for modifying the result of the selected depth operation such that it is suitable for use in an alpha blending operation.

2. Apparatus according to claim 1 in which the object being shaded is of variable translucency and the blending value selected is dependent on the translucency of the object at a pixel.

3. Apparatus according to claim 2 in which translucent objects are first divided into front and rear facing portions, the rear facing portions are firstly supplied to the depth comparison means and the depth operation selecting means updates the depth storing means if the rear facing surface is closer to the eye than the currently stored surface, the front facing surfaces are then supplied to the depth storing means and the depth operation selection means updates the depth store with the result of a subtraction of the currently stored depth from the new depth, and the blending value is in dependence on this value.

4. Apparatus according to claim 3 in which the blending value selected is proportional to the result of the subtraction.

5. Apparatus according to claim 2 in which an object applied to the depth operation selection means subsequently generates an alpha value for use in the means for alpha blending.

6. Apparatus according to claim 1 in which an object applied to the depth operation selection means is used to construct depth buffer values for use during further use of depth comparison means.

7. Apparatus for shading a three dimensional computer graphic image which includes objects which are at least partially translucent comprising:

a) means for supplying data defining objects to be inserted into the image;

b) means for storing depth data for objects in the image;

c) means for comparing the depth of an object to be inserted into the image with currently stored depth data for a pixel, at each pixel covered by the object;

d) means for selecting a blending value to combine the object with the image in dependence on the result or the comparison and on the translucency of the object at that pixel;

e) means for combining the object with the image in dependence on the selected blending value.

8. A method for shading in three dimensional computer graphic image which includes objects which are at least partially translucent comprising the steps of:

a) supplying data defining objects to be inserted into the image;

b) storing depth data or objects in the image;

c) comparing the depth of an object to be inserted into the image with currently stored depth data for a pixel, at each pixel covered by the object;

d) selecting a blending value to combine the object with the image in dependence on the result of the comparison and on the translucency of the object at that pixel;

e) combining the object with the image in dependence on the selected blending value.