GPUMaterial: Fix color ramp node with constant interpolation

Color ramp with constant interpolation must bypass texture filtering and
use nearest neighboor sampling in order to appear correctly sharp.

This patch use a GLSL hack to use nearest sampling on thoses particular
color band.

2 files changed, 15 insertions, 2 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_material.glsl b/source/blender/gpu/shaders/gpu_shader_material.glsl
index 91104fe51bd..40aba1cc004 100644
--- a/source/blender/gpu/shaders/gpu_shader_material.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_material.glsl
@@ -818,6 +818,12 @@ void valtorgb(float fac, sampler1DArray colormap, float layer, out vec4 outcol,
 	outalpha = outcol.a;
 }
 
+void valtorgb_nearest(float fac, sampler1DArray colormap, float layer, out vec4 outcol, out float outalpha)
+{
+	outcol = texelFetch(colormap, ivec2(fac * textureSize(colormap, 0).x, layer), 0);
+	outalpha = outcol.a;
+}
+
 void rgbtobw(vec4 color, out float outval)
 {
 	vec3 factors = vec3(0.2126, 0.7152, 0.0722);
diff --git a/source/blender/nodes/shader/nodes/node_shader_valToRgb.c b/source/blender/nodes/shader/nodes/node_shader_valToRgb.c
index 00940b5acaf..5f583e1e29b 100644
--- a/source/blender/nodes/shader/nodes/node_shader_valToRgb.c
+++ b/source/blender/nodes/shader/nodes/node_shader_valToRgb.c
@@ -65,12 +65,19 @@ static void node_shader_init_valtorgb(bNodeTree *UNUSED(ntree), bNode *node)
 
 static int gpu_shader_valtorgb(GPUMaterial *mat, bNode *node, bNodeExecData *UNUSED(execdata), GPUNodeStack *in, GPUNodeStack *out)
 {
+	struct ColorBand *coba = node->storage;
 	float *array, layer;
 	int size;
 
-	BKE_colorband_evaluate_table_rgba(node->storage, &array, &size);
+	BKE_colorband_evaluate_table_rgba(coba, &array, &size);
 	GPUNodeLink *tex = GPU_texture_ramp(mat, size, array, &layer);
-	return GPU_stack_link(mat, node, "valtorgb", in, out, tex, GPU_uniform(&layer));
+
+	if (coba->ipotype == COLBAND_INTERP_CONSTANT) {
+		return GPU_stack_link(mat, node, "valtorgb_nearest", in, out, tex, GPU_uniform(&layer));
+	}
+	else {
+		return GPU_stack_link(mat, node, "valtorgb", in, out, tex, GPU_uniform(&layer));
+	}
 }
 
 void register_node_type_sh_valtorgb(void)