avstenit

12-03-2013, 06:50 AM

I am displaying a geometry (file format: .stl) with OpenGL (PyOpenGL and Python). Geometry data has the form (http://en.wikipedia.org/wiki/STL_%28file_format%29)and is assembled from triangles. I save to VBO data of; vertices, normals and colors. As the normal is only defined per 3 vertices (triangle) and I define color vector for every vertex, the data in VBO has the form:

VBO = [v1x, v1y, v1z,...vNx, vNy, vNz,

n1x, n1y, n1z,...nNx, nNy, nNz,

R1, G1, B1,...RN, GN, BN]

In words; first I save all vertices, then I "append" (use of glBufferSubData) all normals (number of normals is 3-times less then number of vertices and vertice's colors) and then I append color vectors of each vertex. I would like to know if this is good idea, as I have problems painting each vertex in different color. The code for drawing is:

glPushMatrix()

glEnableClientState(GL_VERTEX_ARRAY)

glVertexPointer(3,

GL_FLOAT,

0,

None)

glEnableClientState(GL_COLOR_ARRAY)

glColorPointer(3,

GL_UNSIGNED_BYTE,

0,

self.data_size_vertices+self.data_size_normals)

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, self.vbo_id)

glDrawArrays(GL_TRIANGLES,

0,

self.N_vertices)

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0) # reset

glDisableClientState(GL_COLOR_ARRAY)

glDisableClientState(GL_VERTEX_ARRAY)

glPopMatrix()

I think I am having problems with glColorPointer(). Can someone point out the problem? I have also seen two more ways to save the data to VBO:

create separate VBO for vertices, VBO for normals and VBO for colors

one VBO but has the form: [v1, c1, v2, c2, v3, c3, n1, ....]

Is any of this two a better solution (more common in practice)? And do I have to assign a normal of triangle to each vertex although it is the same (for 3 vertices that define a triangle)? As I would like to get the display as shown below (left: current state, middle: plan, right: ideal - the point is the shading of surfaces), I would like to ask you to give me some directions about how to achieve this (using shaders).

1191

VBO = [v1x, v1y, v1z,...vNx, vNy, vNz,

n1x, n1y, n1z,...nNx, nNy, nNz,

R1, G1, B1,...RN, GN, BN]

In words; first I save all vertices, then I "append" (use of glBufferSubData) all normals (number of normals is 3-times less then number of vertices and vertice's colors) and then I append color vectors of each vertex. I would like to know if this is good idea, as I have problems painting each vertex in different color. The code for drawing is:

glPushMatrix()

glEnableClientState(GL_VERTEX_ARRAY)

glVertexPointer(3,

GL_FLOAT,

0,

None)

glEnableClientState(GL_COLOR_ARRAY)

glColorPointer(3,

GL_UNSIGNED_BYTE,

0,

self.data_size_vertices+self.data_size_normals)

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, self.vbo_id)

glDrawArrays(GL_TRIANGLES,

0,

self.N_vertices)

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0) # reset

glDisableClientState(GL_COLOR_ARRAY)

glDisableClientState(GL_VERTEX_ARRAY)

glPopMatrix()

I think I am having problems with glColorPointer(). Can someone point out the problem? I have also seen two more ways to save the data to VBO:

create separate VBO for vertices, VBO for normals and VBO for colors

one VBO but has the form: [v1, c1, v2, c2, v3, c3, n1, ....]

Is any of this two a better solution (more common in practice)? And do I have to assign a normal of triangle to each vertex although it is the same (for 3 vertices that define a triangle)? As I would like to get the display as shown below (left: current state, middle: plan, right: ideal - the point is the shading of surfaces), I would like to ask you to give me some directions about how to achieve this (using shaders).

1191