Rendering two objects in OpenGL ES - ios

Question

Im trying to add two objects, which is created from one part, but since i need to color each part i have seperated them. I have tried to render one part which works, but i have afterwards tried to render both which renders nothing.
glGenVertexArraysOES(1, &_boxVAO);
glBindVertexArrayOES(_boxVAO);
int sizeOfFaces = myMesh_m.faces.size() * sizeof(ObjMeshFace);
glGenBuffers(1, &_boxBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _boxBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeOfFaces, &(myMesh_m.faces[0]), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), 0);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), (void*)(sizeof(Vector3f) + sizeof(Vector2f)));
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(2);
sizeOfFaces = myMesh_p.faces.size() * sizeof(ObjMeshFace);
glGenBuffers(1, &_boxBuffer_sec);
glBindBuffer(GL_ARRAY_BUFFER, _boxBuffer_sec);
glBufferData(GL_ARRAY_BUFFER, sizeOfFaces, &(myMesh_p.faces[0]), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), 0);
glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), (void*)(sizeof(Vector3f) + sizeof(Vector2f)));
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(2);
glBindVertexArrayOES(0);
Draw:
glBindVertexArrayOES( _boxVAO);
glUniform2fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, color);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, GL_FALSE, _modelViewProjectionMatrix.m);
glDrawArrays(GL_TRIANGLES, 0, pointerSize_m*3);
Shader.vsh
attribute vec4 position;
attribute vec3 normal;
varying lowp vec4 colorVarying;
uniform mat4 modelViewProjectionMatrix;
uniform mat3 normalMatrix;
void main()
{
vec3 eyeNormal = normalize(normalMatrix * normal);
vec3 lightPosition = vec3(1.0, 1.0, 1.0);
vec4 diffuseColor = vec4(1, 0.4, 1.0, 1.0);
float nDotVP = max(0.0, dot(eyeNormal, normalize(lightPosition)));
colorVarying = diffuseColor * nDotVP;
gl_Position = modelViewProjectionMatrix * position;
}
Shader.fsh
//varying lowp vec4 colorVarying;
uniform lowp vec4 color;
void main()
{
// gl_FragColor = colorVarying;
gl_FragColor = color;
}
Why does this fail? Furthermore how do i color each object?

Answer 1

This goes on the draw method. The color declaration should be outside the drawing method unless you have a variable that changes. (Like I have this inside the drawing loop because I would have "x" instead of 200)
GLfloat color[4];
color[0] = 200/255.0;
color[1] = 0.0/255.0;
color[2] = 0.0/255.0;
color[3] = 255.0/255.0;
GLfloat colorOther[4];
color[0] = 50/255.0;
color[1] = 0.0/255.0;
color[2] = 0.0/255.0;
color[3] = 255.0/255.0;
glUseProgram(_programBorder);
glBindVertexArrayOES(_vaoBorder);
glUniform2fv(uniforms[UNIFORM_COLOR_BORDER], 1, color);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX_BORDER], 1, GL_FALSE, _modelViewProjectionMatrix.m);
glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_SHORT, 0);
//Modify the model projection matrix to change the position of the object
glUniform2fv(uniforms[UNIFORM_COLOR_BORDER], 1, colorOther);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX_BORDER], 1, GL_FALSE, _modelViewProjectionMatrix.m);
glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_SHORT, 0);
The fragment shader has to have the uniform like this:
uniform lowp vec4 color;
void main()
{
gl_FragColor = color;
}
And dont forget to link this uniform properly on your program creation methods.

Answer 2

I know this is a little late to add to the mix, but I was just looking at the answer and it didn't work for me - I had a black square, however I changed
glUniform2fv(uniforms[UNIFORM_COLOR_BORDER], 1, color);
to
glUniform4fv(uniforms[UNIFORM_COLOR_BORDER], 1, color);
And it works now. Should this be 4, as there are 4 values in a colour or is my code messed up elsewhere that this works? :P