I’m very puzzled by texture coordinate in collada. I draw a cube in sketchup and with material mapped to one plane just for test. I find it is very strange that there are UV values out of range of [0,1], and these value seems the same with the vertex of the cube but not exactly. So how can extract useful datas from these UV datas to describe the texture coordinate in [0,1]? i think the UV texture coordinate should be in [0,1] not others. Could anyone help me? Any reference will be OK.
Texture units have wrapping modes to handle coordinates outside the range [0,1]. Values outside that range can cause the image to repeat, clap, use a specified border color, etc…
I know how to extract the vertex and it’s normal vector , but i dosen’t know how to get texture coordinate that could be used in glTexPointer.
Could you give me more detail?
Thank you
All <input> parsing is done the same way, so if you know how to do one semantic you should be able to write functiions that do the others.
The TEXCOORD input semantic samples texture coordinates in the order S, T, P, Q for 1D to 4D coordinates. In your case the <source> supplies 2D (S,T) coordinates. The first value sampled for (S,T) is [-178.350505,121.322840].
The first index vectors of the
element that are used to sample successive values from the inputs are:
[0,0,0]
[1,0,1]
[2,0,2]
etc… Your TEXCOORD input has on offset of 2 (values of [0,1,2]) resulting in sampled TEXCOORD values of:
The “set” attribute distinguishes vertex attributes that belong in different logical groupings (e.g. multi-texture use cases). In other words each vertex is built from base VERTEX attributes plus zero or more sets of other attributes (e.g NORMAL, TEXCOORD, etc.). In your case you only have one logical grouping (TEXCOORD).
Note: COLLADA distinguishes between TEXCOORD (texture coordinates) and UV (generic parameters).
i still doesn’t know why these texture coordinates are out of [0,1]. When i want to map the same texture in OpenGL, i read the picture and generate texture, how can set the correct texture coordinate for every vertex?
if i set the first vertex’s texture coordinate ST1: [-178.350505,121.322840] , i think it cann’t work.
i got this file from sketchup , may some problems in sketchup ?
Just use the values for each vertex as supplied in the .dae document.
The material should say how the texture wraps on the geometry, whether it repeats or clamps. Can you post the <material> and <effect> that Sketchup exported? That will show the answer.
If it doesn’t have the texture wrapping mode explicitly within a <profile_GLSL> or as an extra or parameter in <profile_COMMON> then Sketchup must assume one setting all the time for GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T. You can try using either GL_CLAMP or GL_REPEAT to see which one works.
Just like you say, i could use these texture coordinates directly. I will try but i don’t think it will work. In fact, i just map one face of the cube with texture, why are there 24 pairs of texture coordinates? I still cann’t understand.
In your Sketchup example, the <triangles> element assembles 12 triangle primitives from a pool of: 8 positions, 6 normals, and 24 texcoords.
The position input [index 0] sample ranges from 0 to 7.
The normal input [index 1] sample ranges from 0 to 5.
The texcoord input [index 2] sample ranges from 0 to 23.
I’ve formatted the triangle primitives into rows of three vertexes so that you can see them better: