OK, now we're going to combine two shapes into one! This is called a union. The cool thing about distance fields is that we only need to work with the distance here: you're just finding the closer of the two distances.
You can do this with a single one of GLSL's builtin functions.
{"bannedTokens":[],"prefix":"vec3 draw_line(float d);\nfloat draw_solid(float d);\nvec3 draw_distance(float d, vec2 p);\n","suffix":"vec3 draw_line(float d) {\n const float aa = 3.0;\n const float thickness = 0.0025;\n return vec3(smoothstep(0.0, aa / iResolution.y, max(0.0, abs(d) - thickness)));\n}\n\nfloat draw_solid(float d) {\n return smoothstep(0.0, 3.0 / iResolution.y, max(0.0, d));\n}\n\nvec3 draw_distance(float d, vec2 p) {\n float t = clamp(d * 0.85, 0.0, 1.0);\n vec3 grad = mix(vec3(1, 0.8, 0.5), vec3(0.3, 0.8, 1), t);\n\n float d0 = abs(1.0 - draw_line(mod(d + 0.1, 0.2) - 0.1).x);\n float d1 = abs(1.0 - draw_line(mod(d + 0.025, 0.05) - 0.025).x);\n float d2 = abs(1.0 - draw_line(d).x);\n vec3 rim = vec3(max(d2 * 0.85, max(d0 * 0.25, d1 * 0.06125)));\n\n grad -= rim;\n grad -= mix(vec3(0.05, 0.35, 0.35), vec3(0.0), draw_solid(d));\n\n return grad;\n}\n","question":"uniform vec2 iResolution;\nuniform float iGlobalTime;\n\n//\n// Get the distance field of two circles together in\n// a single function.\n//\nfloat distanceField(vec2 point, vec2 origin1, vec2 origin2, float radius) {\n float d1 = length(point - origin1) - radius;\n float d2 = length(point - origin2) - radius;\n\n return 0.0;\n}\n\nvoid main() {\n vec2 uv = 2.0 * gl_FragCoord.xy / iResolution.xy - 1.0;\n vec2 origin = vec2(sin(iGlobalTime * 0.3) * 0.3);\n float radius = (sin(iGlobalTime * 0.25) * 0.5 + 0.5) * 0.3 + 0.05;\n float dist = distanceField(uv, origin, -origin, radius);\n\n gl_FragColor = vec4(draw_distance(dist, uv), 1);\n}\n","solution":"uniform vec2 iResolution;\nuniform float iGlobalTime;\n\nfloat distanceField(vec2 point, vec2 origin1, vec2 origin2, float radius) {\n float d1 = length(point - origin1) - radius;\n float d2 = length(point - origin2) - radius;\n return min(d1, d2);\n}\n\nvoid main() {\n vec2 uv = 2.0 * gl_FragCoord.xy / iResolution.xy - 1.0;\n vec2 origin = vec2(sin(iGlobalTime * 0.3) * 0.3);\n float radius = (sin(iGlobalTime * 0.25) * 0.5 + 0.5) * 0.3 + 0.05;\n float dist = distanceField(uv, origin, -origin, radius);\n\n gl_FragColor = vec4(draw_distance(dist, uv), 1);\n}\n","name":"09-combining-shapes"}