OpenGL ES on iOS Multiple VBOs without Indices - ios

Question

In my app I have a view that renders STL files. STL files are essentially a list of triangle vertices with normals, they have no indices.
Every tutorial that I have found explains how to use multiple VBOs but with Indices and when I try using drawArrays rather than drawElements it doesn't work. I'm new to OpenGL and would really appreciate it if someone could provide code examples for using multiple VBOs for setup and drawing them without indices.
Here is how I am trying to do this now to no avail. SetupGL:
[EAGLContext setCurrentContext:self.context];
[self loadShaders];
self.effect = [[GLKBaseEffect alloc] init];
self.effect.light0.enabled = GL_TRUE;
self.effect.light0.diffuseColor = GLKVector4Make(.05f, .55f, 1.0f, 1.0f);
glEnable(GL_DEPTH_TEST);
glClearColor(0.88f, 0.88f, 0.88f, 1.0f);
//---- First Vertex Array Object --------
glGenVertexArraysOES(1, &_vertexArray);
glBindVertexArrayOES(_vertexArray);
glBindVertexArrayOES(_vertexArray);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, vertCount*sizeof(verticesBuff) * 3 * 2, verticesBuff, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(12));
//----- Second Vertex Array Object ----------
glGenBuffers(1, &_gridVertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _gridVertexBuffer);
glBufferData(GL_ARRAY_BUFFER, gridVertCount*sizeof(gridVerticesBuff) * 3 * 2, NULL, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(12));
glBindBuffer(GL_ARRAY_BUFFER,0);
glBindVertexArrayOES(0);
And this is my draw code:
glBindVertexArrayOES(_vertexArray);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glUseProgram(_program);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glDrawArrays(GL_TRIANGLES, 0, vertCount);
///////// second VBO and shader program:
glBindBuffer(GL_ARRAY_BUFFER, _gridVertexBuffer);
glUseProgram(_program);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glDrawArrays(GL_TRIANGLES, 0, 108);
Also, here is code that I was using before that doesn't render both the arrays but it does render one (verticesBuff). SetupGL:
[EAGLContext setCurrentContext:self.context];
[self loadShaders];
self.effect = [[GLKBaseEffect alloc] init];
self.effect.light0.enabled = GL_TRUE;
self.effect.light0.diffuseColor = GLKVector4Make(.05f, .55f, 1.0f, 1.0f);
glEnable(GL_DEPTH_TEST);
glClearColor(0.88f, 0.88f, 0.88f, 1.0f);
glGenVertexArraysOES(1, &_vertexArray);
glBindVertexArrayOES(_vertexArray);
glGenBuffers(1, &_gridVertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _gridVertexBuffer);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(12));
glBufferData(GL_ARRAY_BUFFER, 108 * sizeof(gridVerticesBuff), NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(gridVerticesBuff) * 108, gridVerticesBuff);
glGenBuffers(1, &_vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(12));
glBufferData(GL_ARRAY_BUFFER, vertCount*sizeof(verticesBuff) * 3 * 2, NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(verticesBuff) * vertCount * 3, verticesBuff);
glBindVertexArrayOES(0);
And here is the draw code:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (loaded) {
// Render the object with GLKit
[self.effect prepareToDraw];
glBindVertexArrayOES(_gridVertexArray);
glBindBuffer(GL_ARRAY_BUFFER, _gridVertexBuffer);
glDrawArrays(GL_TRIANGLES, 0, 108);
glBindVertexArrayOES(_vertexArray);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glDrawArrays(GL_TRIANGLES, 0, vertCount);
}

Answer 1

It is tough to know exactly what is wrong without seeing your code, but if you follow these general steps you should be able to figure it out. There is little difference between indexed and flat data. Using VBOs will be easier if you understand what they are doing. Essentially VBOs allow you to preupload common vertex data onto the graphics card so it doesn't have to be reploaded every draw call. With that in mind you need to think about how to pack all the vertex data used in a normal draw call into a single memory buffer.
Create Buffer:
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, totalBufferSize, NULL, GL_STATIC_DRAW); /* totalBufferSize is sizeof vertices buffer + sizeof normals buffer */
glBufferSubData(GL_ARRAY_BUFFER, 0, vertexBufferSize, vertexBuffer); /* offset 0 */
glBufferSubData(GL_ARRAY_BUFFER, vertexBufferSize, normalBufferSize, normalBuffer); /* offset vertexbufferSize */
Draw Buffer:
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(VERTEX_ATTRIB ..., ((char*)NULL) + 0); /* start at beginning (0 offset) of the vertex buffer */
glVertexAttribPointer(NORMAL_ATTRIB ..., ((char*)NULL) + vertexBufferSize); /* start at normal subdata (offset vertexBufferSize) of the vertex buffer */
glDrawArrays(..., vertexCount);
The (char*)NULL thing may look a little weird. Instead of passing in a pointer to a buffer in RAM, you are passing in an offset into the currently bound VBO. The arguments of the function still require a pointer so the address of the pointer is used as an offset. Understand NULL is 0 and treat the code as if (char*)NULL + is not there.