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DallyLama

OpenGL Drawing the inside of a cube

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Hello All, I'm kinda a beginner in openGL and I'm trying to draw the inside of a room using openGLES, what I've done so far was that... I create a cube [-1,1]x[-1,1]x[-1,1] and since on my platform I don't have support for most of the openGL API i created my own projection Matrix. Using only my projection Matrix (built like every other openGL matrices) assuming the camera is in the origin and glViewport i rendered the cube, but it looks horrible I only see one wall and it is all flattened, it doesn't have that nice 3D feel to it. I did switch the normals so it will look on the inside but I feel like im doing something fundamentally wrong... Any tips, ideas tutorial or links pointing to the right direction will be gladly Appreciated. Thx all.

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how are you rdrawing the cube? reversing the direction you pass the vertices in (or indices if your doing it that way) will change the faces to point inwards instead of outwards. Otherwise you can change full face to back
glCullFace(GL_BACK); (I think thats it, you could disable culling enritly too).

I would advise againstmessing with the culling though.

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If your cube looked flattened then it could be either of the following.

(1) The vertices are defined properly.
(2) The projection matrix is not defined properly.

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Quote:
Do you mean you see the walls, just not the corners/edges? If so, did you enable lighting?


Yes that is exactly what I mean. I do my lightning inside the fragment shader, I don't use any of the GLstates or predefined attributes, I pass it all manually!

Quote:
how are you rdrawing the cube? reversing the direction you pass the vertices in (or indices if your doing it that way) will change the faces to point inwards instead of outwards.


As I said before I do my own attributes calculation's that means normal's too,
And no cullMode is enabled at least I hope so. does openGL does defualt culling?

Quote:
If your cube looked flattened then it could be either of the following.

(1) The vertices are defined properly.
(2) The projection matrix is not defined properly.


here is the definition of my projection matrix and the definition of the cube:


//the cube:
#define VAL 1.0
#define M_VAL -VAL

glBindTexture(GL_TEXTURE_2D, texture[0]);
float cube_position[]= {
M_VAL, M_VAL, VAL , VAL , M_VAL, VAL , M_VAL, VAL , VAL ,
VAL , M_VAL, VAL , VAL , VAL , VAL , M_VAL, VAL , VAL ,

M_VAL, VAL , VAL , VAL , VAL , VAL , M_VAL, VAL , M_VAL,
VAL , VAL , VAL , VAL , VAL , M_VAL, M_VAL, VAL , M_VAL,

M_VAL, VAL , M_VAL, VAL , VAL , M_VAL, M_VAL, M_VAL, M_VAL,
VAL , VAL , M_VAL, VAL , M_VAL, M_VAL, M_VAL, M_VAL, M_VAL,

M_VAL, M_VAL, M_VAL, VAL , M_VAL, M_VAL, M_VAL, M_VAL, VAL ,
VAL , M_VAL, M_VAL, VAL , M_VAL, VAL , M_VAL, M_VAL, VAL ,

VAL , M_VAL, VAL , VAL , M_VAL, M_VAL, VAL , VAL , VAL ,
VAL , M_VAL,M_VAL, VAL , VAL , M_VAL, VAL , VAL , VAL ,

M_VAL, M_VAL, M_VAL, M_VAL, M_VAL, VAL , M_VAL, VAL ,M_VAL,
M_VAL, M_VAL, VAL , M_VAL, VAL , VAL , M_VAL, VAL , M_VAL };

float cube_normal[]= {
0, 0, 1.0f, 0, 0, 1.0f, 0, 0, 1.0f,
0, 0, 1.0f, 0, 0, 1.0f, 0, 0, 1.0f,

0, 1.0f, 0, 0, 1.0f, 0, 0, 1.0f, 0,
0, 1.0f, 0, 0, 1.0f, 0, 0, 1.0f, 0,

0, 0, -1.0f, 0, 0, -1.0f, 0, 0, -1.0f,
0, 0, -1.0f, 0, 0, -1.0f, 0, 0, -1.0f,

0, -1.0f, 0, 0, -1.0f, 0, 0, -1.0f, 0,
0, -1.0f, 0, 0, -1.0f, 0, 0, -1.0f, 0,

1.0f, 0, 0, 1.0f, 0, 0, 1.0f, 0, 0,
1.0f, 0, 0, 1.0f, 0, 0, 1.0f, 0, 0,

-1.0f, 0, 0, -1.0f, 0, 0, -1.0f, 0, 0,
-1.0f, 0, 0, -1.0f, 0, 0, -1.0f, 0, 0,
};

float cube_uvs[] = {
M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

M_ONE, M_ONE, ONE , M_ONE, M_ONE, ONE,
ONE , M_ONE, ONE , ONE, M_ONE, ONE,

};

// the projection matrix

void gl2_projection(float* mat, float n, float r, float t, float f)
{
gl2_identity(mat);
mat[0] = n/r;
mat[5] = n/t;
mat[10] = -(f+n)/(f-n);
mat[11] = -(2*f*n)/(f-n);
mat[14] = -1;
mat[15] = 0;

}

//drawing function

//defining the transformations
gl2_identity(projection_matrix);
gl2_identity(modelview_matrix);
gl2_projection(projection_matrix, 0.1, 2.0, 2.0 , 5.0);
gl2_rotate(modelview_matrix,mAngle,1.0f,1.0f,1.0f);
MulMatrix(projection_matrix,modelview_matrix,mvp_matrix);
glViewport(0,0,480,800);

// passing all the necessary attributes to the sahders...

//drawing

int mFirstIndex = 0;
int mStripCount = 12;

for(int i = 0; i < mStripCount; i++)
{
glDrawArrays(GL_TRIANGLE_STRIP, mFirstIndex, 3);
mFirstIndex += 3;
}



And to all of you great thanks


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I see you're rotating the camera to see the edges/corners, don't you?

Could you post your shader code?


One thing wrt. your normals:

Your first wall is placed at positive z (VAL) and its normals also point in positive z direction (0,0,1). The opposite wall is located at negative z (M_VAL) and its normals all point to negative z (0,0,-1).

This means your normals are pointing outwards and a normal lighting calculation would just apply ambient light to the vertices if the camera is located inside the cube.


P.S.: per default backface culling is turned on, but since you see the walls, that should not be your problem.

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Quote:
I see you're rotating the camera to see the edges/corners, don't you?


No this is dead code mAngle is set to 0.

Quote:
Could you post your shader code?


I will post them up later today not near my computer.

Quote:
Your first wall is placed at positive z (VAL) and its normals also point in positive z direction (0,0,1). The opposite wall is located at negative z (M_VAL) and its normals all point to negative z (0,0,-1).


I reverse the normal in the fragment shader... again later today I'll post my shders.

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If you're not rotating the camera it might also just be that the corners/edges lie outside your view frustum. Did you check that?

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Cant Say I have, but since my view frustrum span from [-4,4]x[-4,4]

I believe it should be.

But i will check the math nevertheless.

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shader code attached im trying to make deferred shading so ill just attach the lighting pass fragment shader...


#define MAX_LIGHTS 20


#define COSSPOTCUTOFF 0.988 // cos(pi/12)

uniform vec3 lightDirection[MAX_LIGHTS];
//uniform vec3 spotDirection[MAX_LIGHTS];
uniform vec3 lightColor[MAX_LIGHTS];

uniform int maxLights;

uniform sampler2D Env,normalTex,posTex;

varying vec2 vTexCoord;

const vec4 red = vec4(1.0, 0.0, 0.0 ,1.0);
const vec4 blue = vec4(0.0, 0.0, 1.0 ,1.0);
const vec4 green = vec4(0.0, 1.0, 0.0 ,1.0);

void main(void)
{
vec3 v_eyePosition = vec3(0.0,0.0,-25.0);

// sampling the pre made textures
//vec3 normal = texture2D( normalTex, vTexCoord ).xyz;
vec4 t = texture2D( normalTex, vTexCoord );
t =( t*2.0)-vec4(1.0,1.0,1.0,1.0); // transforming back to the normal range

vec3 normal = t.xyz;

vec4 pos = texture2D( posTex, vTexCoord );
pos = (pos*2.0) - vec4(1.0,1.0,1.0,1.0);
vec4 texColor = texture2D( Env, vTexCoord )*1.5;

vec4 diffuse;
vec4 color = vec4(0.1, 0.1, 0.1, 1.0); //this is the ambient term
vec4 specular;
normal = normalize(normal);
vec3 eyeVector = normalize((pos*10.0).xyz - v_eyePosition);
float p = 0.0;
vec4 dif;
for (int i = 0; i < maxLights; i++)
{
//i =;
vec3 lightDir = (pos*10.0).xyz - (lightDirection*20.0);
float NdotL = -dot(normalize(-lightDirection),normal);
//p = NdotL;
if (NdotL > 0.0)
{
float spotEffect = dot(normalize(-lightDirection), normalize(lightDir));
if (spotEffect > COSSPOTCUTOFF)
{

//attanuation factors
spotEffect = pow(spotEffect, 80.0);
float att = spotEffect / (0.02 * length(lightDir));
p = att;


vec3 ref = reflect(normalize(lightDir), normal);

diffuse = NdotL*vec4(lightColor,1.0); //diffuse term

float RdotE = max(dot(-normalize(ref), eyeVector),0.0);
specular = pow(RdotE, 35.0)*vec4(lightColor,1.0); //specular term
color += att * (diffuse + specular);
dif = color;
}
}
}
gl_FragColor = texColor*color;
}




just to explain the array lightDirection is actually the positions of the spotlights, and all the spot direction are the direction between the position and the origin

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      creates a special rotation-translation matrix that moves and rotates the grid away from the origin so that when i finally
      normalize all the vertices on my vertex shader i can get a perfect sphere.
      T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
      the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
      The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
      The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as `r_Grid'.
      // spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The `r_ModelViewProjection' matrix is generated on the CPU in this manner.
      // No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
      Each frame i'm rendering each node by sending the generated matrices this way.
      // set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
      Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
      of the planet the rounding errors start to kick in giving me that lovely stairs effect.
      I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
      getting rid of those rounding errors.
       
      My question is how can i achieve this relative to camera rendering in my scenario here?
      I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
      I only use double on the CPU side where i also do most of the matrix multiplications.
      As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).
       
      Thank you for your suggestions!
       
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