# OpenGL Drawing the inside of a cube

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DallyLama    100
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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Nanoha    2682
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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cgrant    1826
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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Lord_Evil    680
Do you mean you see the walls, just not the corners/edges? If so, did you enable lighting?

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DallyLama    100
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 -VALglBindTexture(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 matrixvoid 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 transformationsgl2_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...//drawingint 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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Lord_Evil    680
I see you're rotating the camera to see the edges/corners, don't you?

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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DallyLama    100
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:

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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Lord_Evil    680
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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DallyLama    100
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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DallyLama    100
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[i]*20.0);		float NdotL = -dot(normalize(-lightDirection[i]),normal);		//p = NdotL;		if (NdotL > 0.0)		{				float spotEffect = dot(normalize(-lightDirection[i]), 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[i],1.0);     //diffuse term										float RdotE = max(dot(-normalize(ref), eyeVector),0.0);					specular = pow(RdotE, 35.0)*vec4(lightColor[i],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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Lord_Evil    680
I didn't thoroughly read your code, but there are some questions:

1. Since your positions/normals should be in eye-space, why do you set another eye position (should be (0,0,0) in eye-space)?

2. Are your light positions/directions given in eye-space to?

3. I assume you use orthographic projection and your frusum spans 8 units in each direction, why do you multiply your fragment positions with 10 (so their z-value could be -10 or 10)? Your maximum depth of 1 (the value in the texture) would correspond to eye-space z = 4 and not 10.

4. Did you try with a directional light first in order to reduce complexity?

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