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Gandalf

Please help me with a OpenGL Light Problem!

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Help! I try to implement a spotlight in a simple OpenGL application. The light is located at (0,0,0). The objects is 15 units away from the lightsource (0,0,-15). There is no light! Everything is almost black. Maybe the range is incorrect. //////////////////// CODE SECTION START ///////////(///////////////////////////////////// GLfloat LightDirection[] = { 0.00f, 0.00f, 1.00f, 0.0f }; //last value toggle dir/pos on off GLfloat LightPosition[] = { 0.00f, 0.00f, 0.00f, 1.0f }; //last value toggle dir/pos on off // Set position glLightfv(GL_LIGHT0, GL_POSITION, LightPosition); // Set direction glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, LightDirection); // Set spread angle glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, (g_PI/8)*g_RADTODEG); // Set intensity. Higher value = more focus ? glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, ((g_PI/8)/2)*g_RADTODEG); // Set attenuation. Here im not sure what I´m doing! glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 1.0f); glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 0.0f); glLightf(GL_LIGHT0, GL_QUADRATIC_ATTENUATION, 0.0f); //////////////////// CODE SECTION END ///////////(///////////////////////////////////// If somebody have succeded to add a spotlight to a scene, please show me some code how to do it! Here is a list on things I already have tried: * Moving x,y,z position up and down. * Used GL_SPOT_DIRECTION to set position (with 4:th value set to 1). * Changed spread angle to almost everything. * Raised/decreased attenuation params without any effect. I''m thinking of commit suicide soon! This driving me crasy! It´s easy in both RM and IM. Gandalf the White

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your target meshes probably have a low vertex count on them - openGL does a per-vertex lighting, meaning each vertex is coloured, not pixel. increase the density of the meshes and it shouls work.

// Set intensity. Higher value = more focus ?

no, just a brighter color for a longer distance

this might help (i''m not promising)

CJ

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But if I decrease the spotlight cone (glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, (g_PI/8)*g_RADTODEG)) then all objects outside the the cone should bee compleatly dark, because I only use one light. This effekt does not show up in my program and that´s why I´m not happy yet.

What other things can be wrong?

Edited by - Gandalf on June 16, 2000 3:40:47 AM

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Hi,

this is some code from my last app where spotlight is ok :


GLfloat light1_position[]={-0.5f, 0.7f, +0.6f, 0.0};
GLfloat spot_direction[]={1.0,1.0,1.0};
....
.....
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT1);
.....
glLightfv(GL_LIGHT1, GL_POSITION,light1_position);
glLightf(GL_LIGHT1, GL_CONSTANT_ATTENUATION,1.5);
glLightf(GL_LIGHT1, GL_LINEAR_ATTENUATION,0.5);
glLightf(GL_LIGHT1, GL_QUADRATIC_ATTENUATION,0.2f);
glLightf(GL_LIGHT1,GL_SPOT_CUTOFF,180);
glLightfv(GL_LIGHT1,GL_SPOT_DIRECTION,spot_direction);
glLightf(GL_LIGHT1,GL_SPOT_EXPONENT,2.0);

hope that help

lunasol


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That works becuase you are setting GL_SPOT_CUTOFF to 180 degree witch means you are not using spotlights at all. Sorry, but that is not what I want.

Gandalf the White

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Shouldn''t the direction of the spotlight be pointing to the screen instead of pointing to you (positive Z-axis)?

You say :
GLfloat LightDirection[] = { 0.00f, 0.00f, 1.00f, 0.0f };

When the spot is at (0,0,0) and the object is at (0,0,-15), the
spot should point to the negative Z-axis.

Hope this helps.

Tatum




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