I had the same problem since A7 in this thread, but in german.

In my experience, d3d_anisotropy acts as a switch and nothing more.

In the meantime, I found a shader solution:

mips_aniso.wmb

Code:
#include <default.c>

FONT* A24bi = "Arial#24bi";

var vAniso = 8.0;

MATERIAL* mtl_anisotropic = 
{
	effect = "
	bool AUTORELOAD;

	float vAniso_var;

	texture entSkin1;
	sampler sAnisotropic = sampler_state {
		Texture = <entSkin1>;
		
		MipFilter = Linear;
		MinFilter = Anisotropic;
		MagFilter = Linear;
		
		MaxAnisotropy = vAniso_var;  
		
		AddressU = Wrap;
		Addressv = Wrap;
	};
	
	technique anisotropic {
		pass one {
			sampler[0] = (sAnisotropic);
		}
	}";
}

VIEW* camera1 = {size_x = 400; size_y = 800; flags = SHOW;}
VIEW* camera2 = {pos_x = 400;	size_x = 400; size_y = 800; flags = SHOW;}

function main() 
{
	vec_set(sky_color,COLOR_BLACK);
	video_window(NULL,NULL,2,NULL);
	video_set(800, 800, 32, 2);
	
	//if (d3d_caps & 2) { d3d_mipmapping = 4; d3d_anisotropy = 16;  printf("d3d_anisotropy active");}
	
	mouse_mode = 4;
	mip_levels = 10;
	d3d_anisotropy = 7;
	d3d_mipmapping = 4;
	
	level_load("mips_aniso.wmb");
	
	camera.flags &= ~SHOW;
	
	vec_set(camera1.x,vector(0,0,150));
	vec_set(camera1.pan,vector(0,-30,0));
	
	vec_set(camera2.x,vector(15000,0,-350));
	vec_set(camera2.pan,vector(0,-30,0));
	
	PANEL* pAniso = pan_create(NULL,0);
	
	pan_setdigits(pAniso,0,10,60,"Anisotropy Level = %.f", A24bi, 1, vAniso);
	
	pan_setstring(pAniso,0,300,  0,A24bi,str_create("mip_levels = 10;"));	
	pan_setstring(pAniso,0, 10, 90,A24bi,str_create("Anisotropy Enabled"));
	pan_setstring(pAniso,0,500, 60,A24bi,str_create("d3d_mipmapping = 4;"));
	pan_setstring(pAniso,0,500, 90,A24bi,str_create("d3d_anisotropy = 7;"));	
	pan_setstring(pAniso,0,500,120,A24bi,str_create("Anisotropy Disabled"));
	
	pan_setslider(pAniso,0,250,60,bmap_fill(bmap_createblack(100,1,32),COLOR_GREY,100),bmap_fill(bmap_createblack(12,32,32),COLOR_RED,100),0,16,vAniso);
	
	set(pAniso, SHOW);
	
	vec_fill(mtl_anisotropic.ambient_blue, 20);
	
	/*while(1) 
	{
		camera1.pan += .1*time_step;
		camera2.pan -= .1*time_step;
		wait(1);
	}*/
}




Regards, Robert

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