CN110738719A - Web3D model rendering method based on visual range hierarchical optimization - Google Patents
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Abstract
The invention discloses an Web3D model rendering method based on visual range hierarchical optimization, which comprises a preprocessing stage, a visibility calculation stage, a working stage and a running stage, wherein the preprocessing stage comprises the steps of (1) generating series space units for a three-dimensional model, ensuring that each block edge of the three-dimensional model is surrounded in the space unit, (2) carrying out visibility calculation on each space units from different viewpoints, recording the visibility of each space unit at different viewpoints, eliminating invisible space units, (3) distributing random numbers for each space unit which is not eliminated, sequencing and storing according to the numbers as key values, and the running stage comprises the steps of (4) dynamically calculating the detail level factors of each space unit along with the change of the viewpoints, and (5) dynamically determining the necessary space units of the current detail level model according to the detail level factors, forming a triangular sequence by the necessary space units and finally sending the triangular sequence to a rendering pipeline for rendering.
Description
Technical Field
The invention relates to the technical field of visualization, in particular to Web3D model rendering methods based on visual range hierarchical optimization.
Background
Three-dimensional (3D) graphics are increasingly used more widely because they represent the world more realistically and intuitively than two-dimensional graphics, and are more easily perceived and accepted by humans, however, rendering three-dimensional graphics requires computers with greater rendering capabilities, especially on the Web side, which is very challenging for large three-dimensional graphics since only CPU resources have been called for rendering in the past.
With the rapid development of related technologies such as computer hardware, computer graphics and the like and the appearance of WebGL, at present, a browser can directly call GPU resources to render, so that rapid rendering of a complex three-dimensional model at the browser end is possible. However, with the rapid increase of the volume of the three-dimensional model, the rendering frame rate of the browser is reduced, and an excessively low frame rate may weaken the real-time interaction of the product, and may even bring a bad experience to the user. Therefore, in order to improve the rendering speed and quality of the browser end for the large-volume model, the rendering of the large-volume model needs to be optimized, and the rendering efficiency is improved on the premise of ensuring the model accuracy.
For example, the concepts of tile structures and detail levels commonly used in map products are very close, namely, according to the scaling condition of the map, the concepts of BVH (bounding volume hierarchy), BSPtree (binary space partitioning tree), Quadtree (quad tree), Octree (Octree) and k-d tree are used as scene partitioning modes frequently used by developers, and the visibility rejection is based on the assumption that invisible geometry and triangles inevitably exist in the large model scene, so that the complexity of the model rendering is reduced, and the consumption of the model rendering is reduced.
Disclosure of Invention
Aiming at the defects in the field and the technical problem of low frame rate of rendering a large-volume model by a browser, the invention provides Web3D model rendering methods based on visual range hierarchical optimization, which can be applied to the fields with 3D visualization requirements, such as intelligent buildings, data centers, health care and the like.
A Web3D model rendering method based on visual range hierarchical optimization comprises the following steps:
a pretreatment stage:
(1) generating series of space cells for the three-dimensional model, ensuring that each edges of the three-dimensional model are enclosed in a space cell;
(2) performing visibility calculation on each space units from different viewpoints, recording the visibility of each space unit at different viewpoints, and removing invisible space units;
(3) distributing random numbers for each space unit which is not removed, and sorting and storing the random numbers as key values;
and (3) an operation stage:
(4) dynamically calculating a level of detail factor for each spatial cell as the viewpoint changes;
(5) and dynamically determining the necessary spatial units of the current detail level model according to the detail level factors, forming the necessary spatial units into a triangular sequence, and finally sending the triangular sequence to a rendering pipeline for rendering.
Preferably, the specific steps of step (1) are:
(1-1) generating an enclosing body of the whole three-dimensional model, namely space units;
(1-2) dividing space units into two subspace units and serving as parent nodes of the two subspace unit nodes;
(1-3) carrying out n times of space division according to the division method in the step (1-2), and finally constructing a recursive included directional bounding box tree by all nodes, wherein the depth of the constructed directional bounding box tree is n, and the number of leaves is 2nI.e. finally dividing the three-dimensional model into 2nA subspace element.
And (3) using the directional bounding box tree to assist in generating the spatial unit, and obtaining spatial unit sets with different fine granularities by giving different depth values. The more spatial cells are generated, the better the visibility calculation effect of step (2) can be made. The present invention divides the three-dimensional model into 128 (the 7 th power of 2) spatial units, i.e., given a depth of n-7. That is, the direction bounding box tree has 128 bottommost leaves, which is 7 in depth.
Preferably, the specific steps of step (2) are:
(2-1) uniformly distributing m cameras around the three-dimensional model as m viewpoints, and sampling the overall shape of the three-dimensional model;
(2-2) performing the visibility calculation by calling a function getVis (cell, camera id), wherein the cell represents any space cells, and the camera id represents any cameras or viewpoints, the function returning the visibility of the specified cameras to the specified space cells;
(2-3) performing visibility calculation for each pairs of camera and spatial cell combination one by one;
and (2-4) eliminating the spatial unit with the visibility of 0.
Visibility determines how many features are visible in a particular spatial cell from a given viewpoint. The calculation formula is as follows:
for each viewpoint camera ID, the features in the spatial cell are rendered four times, wherein rendering is used for setting a depth buffer, the second rendering is used for obtaining the visible pixel number and is recorded as totalPixels, the third rendering is used for rendering all the spatial cells and filling the depth buffer, and finally rendering is used for rendering the current spatial cell again to calculate the pixel number passing the depth test, namely the pixel number not blocked visPixes.
In the present invention, m may be 16.
Preferably, the step (3) comprises the following specific steps:
(3-1) assigning random numbers to each space units which are not removed, and assigning the assigned random numbers as key values of the space units;
and (3-2) performing binary sorting on all the space units according to the key values and then storing the space units.
Preferably, the specific steps of step (4) are:
(4-1) dynamically acquiring the visibilities of any groups of viewpoints and space units acquired in the preprocessing stage, and recording the visibilities as Vis (cell);
(4-2) respectively calculating a detail level factor of each space unit according to Vis (cell) and the distance from the viewpoint to each space units, and recording the detail level factor as factor (lod);
and (4-3) storing the factor (lod) of each space unit in a cache of the video memory.
Preferably, the specific steps of step (5) are:
(5-1) according to the ordered spatial unit sequence obtained in the preprocessing stage, calculating to obtain a least necessary spatial unit to represent the current detail level model, and marking the least necessary spatial unit as Ncell×Factor(lod)；
(5-2) generating a triangle sequence of necessary space units in parallel by using the parallel capability of the GPU;
and (5-3) sending the triangle sequence to a rendering pipeline for rendering.
In step (5-1), NcellThe characteristic number of each space unit is represented, and the first N randomly ordered space units can be selected because the randomness of the space units is ensured in the preprocessing stagecellX factor (lod) features represent the least necessary spatial units under the current viewpoint.
Compared with the prior art, the invention has the main advantages that: according to the invention, by adopting the sight distance layered optimization method, unnecessary space units are removed, and under the condition of not influencing user experience, the complexity of the model is simplified, the transmission flow of the model can be reduced, and the loading efficiency is improved.
Drawings
FIG. 1 is a schematic view of a view distance hierarchical optimization algorithm of the present invention;
FIG. 2 is a schematic diagram of assisted generation of a set of spatial cells using a directional bounding box tree;
FIG. 3 is a schematic diagram of computing the visibility of spatial cells from different viewpoints;
FIG. 4 is a diagram illustrating a hierarchical comparison of details of a three-dimensional model after the optimization process according to an embodiment.
Detailed Description
the invention is further described with reference to the accompanying drawings and specific examples, it being understood that these examples are intended to illustrate the invention only and are not intended to limit the scope of the invention.
The flow of the sight distance layered optimization algorithm of the invention is shown in figure 1 and is divided into a preprocessing stage and an operation stage. The preprocessing stage comprises generation of space units, visibility calculation and random leaf sorting; the run phase includes LOD (level of Detail) selection and generation of triangle sequences.
The embodiment specifically illustrates the above Web3D model rendering method based on the line-of-sight hierarchical optimization, which includes:
a pretreatment stage:
(1) as shown in fig. 2, series of spatial cells are generated for the three-dimensional model, and each edges of the three-dimensional model are ensured to be enclosed in the spatial cells, which includes the following steps:
(1-1) generating an enclosing body of the whole three-dimensional model, namely space units;
(1-2) dividing space units into two subspace units and serving as parent nodes of the two subspace unit nodes;
(1-3) performing space division for 7 times according to the division method in the step (1-2), and finally constructing a recursive directional bounding box tree by all nodes, wherein the depth of the constructed directional bounding box tree is 7, and the number of leaves is 128, namely, the three-dimensional model is finally divided into 128 subspace units.
(2) As shown in fig. 3, performing visibility calculation on spatial units from different viewpoints, recording the visibility of each spatial unit at different viewpoints, and removing invisible spatial units, specifically including the steps of:
(2-1) uniformly distributing 16 cameras around the three-dimensional model as 16 viewpoints, and sampling the overall shape of the three-dimensional model;
(2-2) performing the visibility calculation by calling a function getVis (cell, camera id), wherein the cell represents any space cells, and the camera id represents any cameras or viewpoints, the function returning the visibility of the specified cameras to the specified space cells;
getVis (cell, camera ID) function calculation formula is as follows:
for each viewpoint camera ID, the features in the spatial cell are rendered four times, wherein rendering is used for setting a depth buffer, the second rendering is used for obtaining the visible pixel number and is recorded as totalPixels, the third rendering is used for rendering all the spatial cells and filling the depth buffer, and finally rendering is used for rendering the current spatial cell again to calculate the pixel number passing the depth test, namely the pixel number not blocked visPixes.
(2-3) performing visibility calculation for each pairs of camera and spatial cell combination one by one;
and (2-4) eliminating the spatial unit with the visibility of 0.
(3) Distributing random numbers for each space unit which is not removed, and sorting and storing the random numbers as key values, wherein the specific steps are as follows:
(3-1) assigning random numbers to each space units which are not removed, and assigning the assigned random numbers as key values of the space units;
and (3-2) performing binary sorting on all the space units according to the key values and then storing the space units.
And (3) an operation stage:
(4) with the change of the viewpoint, dynamically calculating the detail level factor of each spatial unit, and the specific steps are as follows:
(4-1) dynamically acquiring the visibilities of any groups of viewpoints and space units acquired in the preprocessing stage, and recording the visibilities as Vis (cell);
(4-2) respectively calculating a detail level factor of each space unit according to Vis (cell) and the distance from the viewpoint to each space units, and recording the detail level factor as factor (lod);
and (4-3) storing the factor (lod) of each space unit in a cache of the video memory.
(5) Dynamically determining the necessary spatial units of the current detail level model according to the detail level factors, forming the necessary spatial units into a triangular sequence, and finally sending the triangular sequence to a rendering pipeline for rendering, wherein the method comprises the following specific steps:
(5-1) according to the ordered spatial unit sequence obtained in the preprocessing stage, calculating to obtain a least necessary spatial unit to represent the current detail level model, and marking the least necessary spatial unit as Ncell×Factor(lod)；NcellThe characteristic number of each space unit is represented, and the first N randomly ordered space units can be selected because the randomness of the space units is ensured in the preprocessing stagecellX factor (lod) features represent the least necessary spatial units under the current viewpoint.
(5-2) generating a triangle sequence of necessary space units in parallel by using the parallel capability of the GPU;
and (5-3) sending the triangle sequence to a rendering pipeline for rendering.
The effect of the model after the operation of the view-distance hierarchical optimization algorithm according to the present embodiment is as shown in fig. 4, the smaller the number of pixels visible in the spatial unit farther from the viewpoint.
Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the above description of the present invention, and equivalents also fall within the scope of the invention as defined by the appended claims.
Claims (6)
1, Web3D model rendering method based on visual range hierarchical optimization, characterized by comprising:
a pretreatment stage:
(1) generating series of space cells for the three-dimensional model, ensuring that each edges of the three-dimensional model are enclosed in a space cell;
(2) performing visibility calculation on each space units from different viewpoints, recording the visibility of each space unit at different viewpoints, and removing invisible space units;
(3) distributing random numbers for each space unit which is not removed, and sorting and storing the random numbers as key values;
and (3) an operation stage:
(4) dynamically calculating a level of detail factor for each spatial cell as the viewpoint changes;
(5) and dynamically determining the necessary spatial units of the current detail level model according to the detail level factors, forming the necessary spatial units into a triangular sequence, and finally sending the triangular sequence to a rendering pipeline for rendering.
2. The method for rendering the Web3D model based on the line-of-sight hierarchical optimization according to claim 1, wherein the step (1) comprises the following specific steps:
(1-1) generating an enclosing body of the whole three-dimensional model, namely space units;
(1-2) dividing space units into two subspace units and serving as parent nodes of the two subspace unit nodes;
(1-3) carrying out n times of space division according to the division method in the step (1-2), and finally constructing a recursive included directional bounding box tree by all nodes, wherein the depth of the constructed directional bounding box tree is n, and the number of leaves is 2nI.e. finally dividing the three-dimensional model into 2nA subspace element.
3. The method for rendering the Web3D model based on the line-of-sight hierarchical optimization according to claim 1, wherein the step (2) comprises the following specific steps:
(2-1) uniformly distributing m cameras around the three-dimensional model as m viewpoints, and sampling the overall shape of the three-dimensional model;
(2-2) performing the visibility calculation by calling a function getVis (cell, camera id), wherein the cell represents any space cells, and the camera id represents any cameras or viewpoints, the function returning the visibility of the specified cameras to the specified space cells;
(2-3) performing visibility calculation for each pairs of camera and spatial cell combination one by one;
and (2-4) eliminating the spatial unit with the visibility of 0.
4. The method for rendering the Web3D model based on the line-of-sight hierarchical optimization according to claim 1, wherein the step (3) comprises the following steps:
(3-1) assigning random numbers to each space units which are not removed, and assigning the assigned random numbers as key values of the space units;
and (3-2) performing binary sorting on all the space units according to the key values and then storing the space units.
5. The method for rendering the Web3D model based on the line-of-sight hierarchical optimization according to claim 1, wherein the step (4) comprises the following steps:
(4-1) dynamically acquiring the visibilities of any groups of viewpoints and space units acquired in the preprocessing stage, and recording the visibilities as Vis (cell);
(4-2) respectively calculating a detail level factor of each space unit according to Vis (cell) and the distance from the viewpoint to each space units, and recording the detail level factor as factor (lod);
and (4-3) storing the factor (lod) of each space unit in a cache of the video memory.
6. The method for rendering the Web3D model based on the line-of-sight hierarchical optimization according to claim 1, wherein the step (5) comprises the following steps:
(5-1) according to the ordered spatial unit sequence obtained in the preprocessing stage, calculating to obtain a least necessary spatial unit to represent the current detail level model, and marking the least necessary spatial unit as Ncell×Factor(lod)；
(5-2) generating a triangle sequence of necessary space units in parallel by using the parallel capability of the GPU;
and (5-3) sending the triangle sequence to a rendering pipeline for rendering.
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| CN111354067A (en) * | 2020-03-02 | 2020-06-30 | 成都偶邦智能科技有限公司 | Multi-model same-screen rendering method based on Unity3D engine |
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