I have a set of textures which I need to draw at different vertices such that every texture is visible.I cannot define a static set of vertices since I load the textures dynamically and I dont know how many textures will be loaded everytime ( i choose them based on a condition).
This is how my code looks as of now.
for(int i=0;i<num_img;i++)
{
glLoadIdentity();
glTranslatef(0.0, 0.0, -3.0);
glRotatef(rot, 1.0, 1.0, 1.0);
glBindTexture(GL_TEXTURE_2D, texture[i]);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glNormalPointer(GL_FLOAT, 0, normals);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}
Is there anyway to dynamically generate vertices that can be passed as final argument of glVertexPointer() ?
Do you know the maximum number of vertices that you will use? Maybe you could create the vertices array to be that maximum size then in the first parameter of glVertexPointer you only pass the number of vertices that you actually use.
Related
I'm using the following code to draw a green line at some specified coordinates
GLfloat colors[] = {0,1,0,1, 0,1,0,0.5};
CGPoint v[] = {{p1.x, p1.y}, {p2.x, p2.y}};
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_LINE_SMOOTH);
glLineWidth(10);
glVertexPointer(2, GL_FLOAT, 0, &v);
glColorPointer(4, GL_FLOAT, 0, &colors);
glDrawArrays(GL_LINE_LOOP, 0, 2);
glDisableClientState(GL_LINE_SMOOTH);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
The problem is that once in a while even if the draw method gets called, the line turns black or does not get drawn entirely. i've checked the coordinates i pass and they seem fine.
Is there something that i'm missing?
GL_LINE_SMOOTH has never been an acceptable argument to glEnableClientState().
It might not be the source of the problem, and you might have noticed it already, but isn't it correct to pass arrays to the functions without '&' or with '[0]'? i.e.
glVertexPointer(2, GL_FLOAT, 0, &v); // --> &v should be v, or &v[0]
glColorPointer(4, GL_FLOAT, 0, &colors); // --> colors, or &colors[0]
Also, glEnable(GL_LINE_SMOOTH); seems the correct syntax.
I´m creating an opengl ES project and I´m trying to show some textures, all works good but the problem is the use of the memory, every 5 seconds increments almost 1 Mb, I think I´m doing something wrong, I´m not using any of this apple recommendations I will tray for sure, but I want to know if my code have some bug, there is how I´m paiting:
// Generate the vertex buffer object (VBO)
glGenBuffers(1, &ui32Vbo);
// Bind the VBO so we can fill it with data
glBindBuffer(GL_ARRAY_BUFFER, ui32Vbo);
// Set the buffer's data
// Calculate verts size: (3 vertices * stride (3 GLfloats per each vertex))
glBufferData(GL_ARRAY_BUFFER, uiSize, verts, GL_STATIC_DRAW);
// Bind the VBO so we can fill it with data
glBindBuffer(GL_ARRAY_BUFFER, ui32Vbo);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 20, 0); // Stride = 20 bytes
glBindTexture(GL_TEXTURE_2D, textID);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 20, (void *)12);
glDrawArrays(GL_TRIANGLE_FAN, 4, 4);
// Bind the VBO so we can fill it with data
glBindBuffer(GL_ARRAY_BUFFER, 0);
Thank you very much!!!
You should generate the vertex buffer object only once, the use it draw.
It seems you create a new one each frame.
I am using point sprites to display a few ten thousand points, each with a different size. It works well, looks great and is quite fast. I'm using a VBO with the coordinates and the sizes in it (4 floats per point).
Here is my display code
glEnable(GL_POINT_SPRITE_OES);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, pointTexture);
glTexEnvi( GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, GL_TRUE );
glEnableClientState(GL_VERTEX_ARRAY);
glBindBuffer(GL_ARRAY_BUFFER, pointVertices);
glVertexPointer(3, GL_FLOAT, 4*sizeof(float), 0);
glEnableClientState(GL_POINT_SIZE_ARRAY_OES);
glPointSizePointerOES(GL_FLOAT,4*sizeof(float),(GLvoid*) (sizeof(GL_FLOAT)*3));
glDrawArrays(GL_POINTS, 0, pointNum);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glDisableClientState(GL_POINT_SIZE_ARRAY_OES);
glDisableClientState(GL_VERTEX_ARRAY);
glDisable(GL_TEXTURE_2D);
glDisable(GL_POINT_SPRITE_OES);
Now, I would also like to be able to zoom in, i.e. use glScalef. Is it possible to change the size of the points accordingly without updating the VBO? glPointSize doesn't have any effect, as I'm using GL_POINT_SIZE_ARRAY_OES.
Yes, use glPointParameter with the GL_POINT_DISTANCE_ATTENUATION parameter.
http://www.khronos.org/opengles/sdk/1.1/docs/man/glPointParameter.xml
It's quite tricky to get right, though.
I'm doing the following:
static GLfloat vertices[3][3] =
{
{0.0, 1.0, 0.0},
{1.0, 0.0, 0.0},
{-1.0, 0.0, 0.0}
};
glColor4ub(255, 0, 0, 255);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawArrays(GL_TRIANGLES, 0, 9);
glDisableClientState(GL_VERTEX_ARRAY);
This works ok:
http://dl.dropbox.com/u/41764/posts/Screen%20shot%202010-03-28%20at%2020.04.56.png
However, if I remove static from vertices and therefore re-create the data on the stack on each rendering, I get the following:
http://dl.dropbox.com/u/41764/posts/Screen%20shot%202010-03-28%20at%2020.06.38.png
This happens both on the simulator and on the device.
Should I be keeping the variables around after I call glDrawArrays?
The reason you're seeing weird results is because you're not drawing what you think you are.
glDrawArrays(GL_TRIANGLES, 0, 9);
This means draw 9 vertices, hence 3 triangles. You only have 3 vertices declared in your array, so what the other 2 triangles will end up being is anybody's guess. You can see in the second picture that you indeed have more than 1 triangle... The data it ends up using is whatever else is on the stack at that time.
glDrawArrays does transfer on call, and I seriously doubt the iPhone would not be compliant on this. It's really basic GL, that (I believe) gets tested for conformance.
You are rendering uninitialized data in both cases. It just happens to look correct in the static case.
The third parameter to glDrawArrays is the number of vertices (which should be 3 in your case because you are trying to draw a single triangle).
You already told the GL that you are specifying 3 GLfloat per vertex (the first parameter of glVertexPointer). So the GL can figure out the total number of GLfloat to expect.
This should work:
GLfloat vertices[3][3] =
{
{0.0, 1.0, 0.0},
{1.0, 0.0, 0.0},
{-1.0, 0.0, 0.0}
};
glColor4ub(255, 0, 0, 255);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableClientState(GL_VERTEX_ARRAY);
I am trying to learn OpenGL on the iPhone using the "Super Bible" but am having trouble porting from OpenGLto OpenGL ES. My understanding is that the glRectf() function is not available in the latter. What is the substitute approach? Any relevant conceptual information would be appreciated as well.
The substitute approach is to draw a triangle strip:
GLfloat texture[] =
{
0, 0,
0, 1,
1, 0,
1, 1
};
GLfloat model[] =
{
0, 0, // lower left
0, h, // upper left
w, 0, // lower right
w, h // upper right
};
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, model);
glTexCoordPointer(2, GL_FLOAT, 0, texture);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
This draws a textured rectangle with width w and height h.
Rather than doing a rect, you just do two triangles.
This is really irrelevant though since GL-ES on the iPhone does not support immediate mode. You need to define all your vertices in an array and use one of the vertex array rendering functions to draw them rather than using the immediate mode functions.