guiding-lines style

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This style is made of three layers. The first layer gathers the guiding lines that were used by the artist to roughly draw the proportions of each part of the body. The artist gently uses a thick charcoal for these lines. For these lines, we use the pyGuidingLinesShader that approximates each stroke by its "tangent". The error of the approximation depends on the size of the original stroke that is approximated: the shorter the stroke, the smaller the error. We wrote two shaders respectively simulating a coarse and a fine level of approximation usig guiding lines. We control the length of the stroke using a splitting operator, based on a 2D curvature evaluation. The split recursively splits each stroke until a stopping condition is reached. This stopping condition produces shorter lines in the fine level case. The last layer contains the final lines, made using a thiner charcoal, and with a higher pressure on the paper. We only applied this style to the lines that were close enough to the viewer in order to simulate the "unfinished" effect.

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