add GPU_SHADER_TEXT for font rendering

With USE_GLSL enabled, GPU_basic_shader(TEXTURE|COLOR) always rendered black. New shader uses a solid color + alpha channel of texture (which in our case is a font glyph). See fragment shader for details.

I prefer this approah -- multiple shaders that each do one thing well (and are easy to read/write/understand), instead of one shader that can do many things given the right options.

source/blender/blenfont/intern/blf.c

@@ -56,7 +56,7 @@
 #include "IMB_colormanagement.h"
 
 #ifndef BLF_STANDALONE
-#include "GPU_basic_shader.h"
+#include "GPU_shader.h"
 #endif
 
 #include "blf_internal_types.h"
@@ -501,7 +501,7 @@ static void blf_draw_gl__start(FontBLF *font, GLint *mode)
 	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
 #ifndef BLF_STANDALONE
-	GPU_basic_shader_bind(GPU_SHADER_TEXTURE_2D | GPU_SHADER_USE_COLOR);
+	GPU_shader_bind(GPU_shader_get_builtin_shader(GPU_SHADER_TEXT));
 #endif
 
 	/* Save the current matrix mode. */
@@ -544,8 +544,9 @@ static void blf_draw_gl__end(GLint mode)
 		glMatrixMode(mode);
 
 #ifndef BLF_STANDALONE
-	GPU_basic_shader_bind(GPU_SHADER_USE_COLOR);
+	GPU_shader_unbind();
 #endif
+
 	glDisable(GL_BLEND);
 }
 

source/blender/gpu/CMakeLists.txt

@@ -130,6 +130,9 @@ data_to_c_simple(shaders/gpu_shader_3D_flat_color_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_smooth_color_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_smooth_color_frag.glsl SRC)
 
+data_to_c_simple(shaders/gpu_shader_text_vert.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_text_frag.glsl SRC)
+
 data_to_c_simple(shaders/gpu_shader_geometry.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_fire_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_smoke_frag.glsl SRC)

source/blender/gpu/GPU_shader.h

@@ -90,6 +90,8 @@ typedef enum GPUBuiltinShader {
 	GPU_SHADER_SMOKE             = 2,
 	GPU_SHADER_SMOKE_FIRE        = 3,
 
+	GPU_SHADER_TEXT,
+
 	/* for simple 2D drawing */
 	GPU_SHADER_2D_UNIFORM_COLOR,
 	GPU_SHADER_2D_FLAT_COLOR,

source/blender/gpu/intern/gpu_shader.c

@@ -58,6 +58,9 @@ extern char datatoc_gpu_shader_3D_flat_color_vert_glsl[];
 extern char datatoc_gpu_shader_3D_smooth_color_vert_glsl[];
 extern char datatoc_gpu_shader_3D_smooth_color_frag_glsl[];
 
+extern char datatoc_gpu_shader_text_vert_glsl[];
+extern char datatoc_gpu_shader_text_frag_glsl[];
+
 extern char datatoc_gpu_shader_fire_frag_glsl[];
 extern char datatoc_gpu_shader_smoke_vert_glsl[];
 extern char datatoc_gpu_shader_smoke_frag_glsl[];
@@ -83,6 +86,8 @@ static struct GPUShadersGlobal {
 		GPUShader *smoke_fire;
 		/* cache for shader fx. Those can exist in combinations so store them here */
 		GPUShader *fx_shaders[MAX_FX_SHADERS * 2];
+		/* for drawing text */
+		GPUShader *text;
 		/* for simple 2D drawing */
 		GPUShader *uniform_color_2D;
 		GPUShader *flat_color_2D;
@@ -610,6 +615,14 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 				        NULL, NULL, NULL, 0, 0, 0);
 			retval = GG.shaders.smoke_fire;
 			break;
+		case GPU_SHADER_TEXT:
+			if (!GG.shaders.text)
+				GG.shaders.text = GPU_shader_create(
+				        datatoc_gpu_shader_text_vert_glsl,
+				        datatoc_gpu_shader_text_frag_glsl,
+				        NULL, NULL, NULL, 0, 0, 0);
+			retval = GG.shaders.text;
+			break;
 		case GPU_SHADER_2D_UNIFORM_COLOR:
 			if (!GG.shaders.uniform_color_2D)
 				GG.shaders.uniform_color_2D = GPU_shader_create(
@@ -777,6 +790,11 @@ void GPU_shader_free_builtin_shaders(void)
 		GG.shaders.smoke_fire = NULL;
 	}
 
+	if (GG.shaders.text) {
+		GPU_shader_free(GG.shaders.text);
+		GG.shaders.text = NULL;
+	}
+
 	if (GG.shaders.uniform_color_2D) {
 		GPU_shader_free(GG.shaders.uniform_color_2D);
 		GG.shaders.uniform_color_2D = NULL;

source/blender/gpu/shaders/gpu_shader_text_frag.glsl

@@ -0,0 +1,14 @@
+
+flat varying vec4 color;
+varying vec2 texcoord;
+
+uniform sampler2D glyph;
+
+void main()
+{
+	// input color replaces texture color
+	gl_FragColor.rgb = color.rgb;
+
+	// modulate input alpha & texture alpha
+	gl_FragColor.a = color.a * texture2D(glyph, texcoord).a;
+}

source/blender/gpu/shaders/gpu_shader_text_vert.glsl

@@ -0,0 +1,16 @@
+
+// TODO(merwin):
+// - use modern GLSL
+// - uniform color, not per vertex
+// - generic attrib inputs (2D pos, tex coord)
+
+flat varying vec4 color;
+varying vec2 texcoord;
+
+void main()
+{
+	gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
+
+	color = gl_Color;
+	texcoord = (gl_TextureMatrix[0] * gl_MultiTexCoord0).st;
+}