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Add subpixel font rendering to the OpenGL backend

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Finally, something besides the software renderer supports it
This commit is contained in:
Clownacy 2019-08-07 22:33:13 +00:00
parent 7e04741c29
commit fc102cd5a5
1 changed files with 86 additions and 18 deletions
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104
src/Backends/Rendering/OpenGL3.cpp
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@ -25,6 +25,7 @@ typedef struct Backend_Glyph
GLuint texture_id;
unsigned int width;
unsigned int height;
BOOL subpixel_mode;
} Backend_Glyph;
typedef struct Coordinate2D
@ -45,10 +46,13 @@ static SDL_GLContext context;
static GLuint program_texture;
static GLuint program_texture_colour_key;
static GLuint program_colour_fill;
static GLuint program_glyph;
static GLuint program_glyph_normal;
static GLuint program_glyph_subpixel_part1;
static GLuint program_glyph_subpixel_part2;
static GLint program_colour_fill_uniform_colour;
static GLint program_glyph_uniform_colour;
static GLint program_glyph_normal_uniform_colour;
static GLint program_glyph_subpixel_part2_uniform_colour;
static GLuint vertex_array_id;
static GLuint vertex_buffer_id;
@ -116,7 +120,7 @@ void main() \
} \
";
static const GLchar *fragment_shader_glyph = " \
static const GLchar *fragment_shader_glyph_normal = " \
#version 150 core\n \
uniform sampler2D tex; \
uniform vec4 colour; \
@ -128,6 +132,29 @@ void main() \
} \
";
static const GLchar *fragment_shader_glyph_subpixel_part1 = " \
#version 150 core\n \
uniform sampler2D tex; \
in vec2 texture_coordinates; \
out vec4 fragment; \
void main() \
{ \
fragment = texture2D(tex, texture_coordinates); \
} \
";
static const GLchar *fragment_shader_glyph_subpixel_part2 = " \
#version 150 core\n \
uniform sampler2D tex; \
uniform vec4 colour; \
in vec2 texture_coordinates; \
out vec4 fragment; \
void main() \
{ \
fragment = colour * texture2D(tex, texture_coordinates); \
} \
";
static void GLAPIENTRY MessageCallback(GLenum source, GLenum type, GLuint id, GLenum severity, GLsizei length, const GLchar *message, const void* userParam)
{
(void)source;
@ -207,8 +234,6 @@ BOOL Backend_Init(SDL_Window *p_window)
glEnable(GL_DEBUG_OUTPUT);
glDebugMessageCallback(MessageCallback, 0);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
@ -230,14 +255,17 @@ BOOL Backend_Init(SDL_Window *p_window)
program_texture = CompileShader(vertex_shader_texture, fragment_shader_texture);
program_texture_colour_key = CompileShader(vertex_shader_texture, fragment_shader_texture_colour_key);
program_colour_fill = CompileShader(vertex_shader_plain, fragment_shader_colour_fill);
program_glyph = CompileShader(vertex_shader_texture, fragment_shader_glyph);
program_glyph_normal = CompileShader(vertex_shader_texture, fragment_shader_glyph_normal);
program_glyph_subpixel_part1 = CompileShader(vertex_shader_texture, fragment_shader_glyph_subpixel_part1);
program_glyph_subpixel_part2 = CompileShader(vertex_shader_texture, fragment_shader_glyph_subpixel_part2);
if (program_texture == 0 || program_texture_colour_key == 0 || program_colour_fill == 0 || program_glyph == 0)
if (program_texture == 0 || program_texture_colour_key == 0 || program_colour_fill == 0 || program_glyph_normal == 0 || program_glyph_subpixel_part1 == 0 || program_glyph_subpixel_part2 == 0)
printf("Failed to compile shaders\n");
// Get shader uniforms
program_colour_fill_uniform_colour = glGetUniformLocation(program_colour_fill, "colour");
program_glyph_uniform_colour = glGetUniformLocation(program_glyph, "colour");
program_glyph_normal_uniform_colour = glGetUniformLocation(program_glyph_normal, "colour");
program_glyph_subpixel_part2_uniform_colour = glGetUniformLocation(program_glyph_subpixel_part2, "colour");
// Set up framebuffer (used for surface-to-surface blitting)
glGenFramebuffers(1, &framebuffer_id);
@ -263,7 +291,9 @@ void Backend_Deinit(void)
{
glDeleteTextures(1, &framebuffer_surface.texture_id);
glDeleteFramebuffers(1, &framebuffer_id);
glDeleteProgram(program_glyph);
glDeleteProgram(program_glyph_subpixel_part2);
glDeleteProgram(program_glyph_subpixel_part1);
glDeleteProgram(program_glyph_normal);
glDeleteProgram(program_colour_fill);
glDeleteProgram(program_texture_colour_key);
glDeleteProgram(program_texture);
@ -491,7 +521,7 @@ void Backend_ScreenToSurface(Backend_Surface *surface, const RECT *rect)
BOOL Backend_SupportsSubpixelGlyph(void)
{
return FALSE; // Per-component alpha is available as an extension, but I haven't looked into it yet
return TRUE;
}
Backend_Glyph* Backend_LoadGlyph(const unsigned char *pixels, unsigned int width, unsigned int height, int pitch, unsigned short total_greys, unsigned char pixel_mode)
@ -501,7 +531,9 @@ Backend_Glyph* Backend_LoadGlyph(const unsigned char *pixels, unsigned int width
if (glyph == NULL)
return NULL;
const int destination_pitch = (width + 3) & ~3; // Round up to the nearest 4 (OpenGL needs this)
const BOOL subpixel_mode = pixel_mode == FONT_PIXEL_MODE_LCD;
const int destination_pitch = ((subpixel_mode ? width * 3 : width) + 3) & ~3; // Round up to the nearest 4 (OpenGL needs this)
unsigned char *buffer = (unsigned char*)malloc(destination_pitch * height);
@ -513,7 +545,22 @@ Backend_Glyph* Backend_LoadGlyph(const unsigned char *pixels, unsigned int width
switch (pixel_mode)
{
// FONT_PIXEL_MODE_LCD is unsupported
case FONT_PIXEL_MODE_LCD:
for (unsigned int y = 0; y < height; ++y)
{
const unsigned char *source_pointer = pixels + y * pitch;
unsigned char *destination_pointer = buffer + y * destination_pitch;
for (unsigned int x = 0; x < width; ++x)
{
for (unsigned int i = 0; i < 3; ++i)
{
*destination_pointer++ = (unsigned char)(pow((*source_pointer++ / 255.0), 1.0 / 1.8) * 255.0);
}
}
}
break;
case FONT_PIXEL_MODE_GRAY:
for (unsigned int y = 0; y < height; ++y)
@ -546,7 +593,7 @@ Backend_Glyph* Backend_LoadGlyph(const unsigned char *pixels, unsigned int width
glGenTextures(1, &glyph->texture_id);
glBindTexture(GL_TEXTURE_2D, glyph->texture_id);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, buffer);
glTexImage2D(GL_TEXTURE_2D, 0, subpixel_mode ? GL_RGB8 : GL_R8, width, height, 0, subpixel_mode ? GL_RGB : GL_RED, GL_UNSIGNED_BYTE, buffer);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
@ -555,6 +602,7 @@ Backend_Glyph* Backend_LoadGlyph(const unsigned char *pixels, unsigned int width
glyph->width = width;
glyph->height = height;
glyph->subpixel_mode = subpixel_mode;
free(buffer);
@ -579,8 +627,6 @@ static void DrawGlyphCommon(Backend_Surface *surface, Backend_Glyph *glyph, long
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, surface->texture_id, 0);
glViewport(0, 0, surface->width, surface->height);
glUseProgram(program_glyph);
glEnable(GL_BLEND);
// Enable texture coordinates, since this uses textures
@ -593,8 +639,6 @@ static void DrawGlyphCommon(Backend_Surface *surface, Backend_Glyph *glyph, long
const GLfloat vertex_top = (y * (2.0f / surface->height)) - 1.0f;
const GLfloat vertex_bottom = ((y + glyph->height) * (2.0f / surface->height)) - 1.0f;
glUniform4f(program_glyph_uniform_colour, colours[0] / 255.0f, colours[1] / 255.0f, colours[2] / 255.0f, 1.0f);
vertex_buffer.texture_coordinates[0].x = 0.0f;
vertex_buffer.texture_coordinates[0].y = 0.0f;
vertex_buffer.texture_coordinates[1].x = 1.0f;
@ -614,7 +658,31 @@ static void DrawGlyphCommon(Backend_Surface *surface, Backend_Glyph *glyph, long
vertex_buffer.vertexes[3].y = vertex_bottom;
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
if (glyph->subpixel_mode)
{
// Here we're going to draw with per-component alpha.
// Since OpenGL doesn't really support this, we have to do it manually:
// Step one: attenuate the destination pixels by the alpha
glBlendFunc(GL_ZERO, GL_ONE_MINUS_SRC_COLOR);
glUseProgram(program_glyph_subpixel_part1);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
// Step two: add the new pixels on top of them
glBlendFunc(GL_ONE, GL_ONE);
glUseProgram(program_glyph_subpixel_part2);
glUniform4f(program_glyph_subpixel_part2_uniform_colour, colours[0] / 255.0f, colours[1] / 255.0f, colours[2] / 255.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
}
else
{
// Here, we just use a regular alpha channel
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glUseProgram(program_glyph_normal);
glUniform4f(program_glyph_normal_uniform_colour, colours[0] / 255.0f, colours[1] / 255.0f, colours[2] / 255.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
}
}
void Backend_DrawGlyph(Backend_Surface *surface, Backend_Glyph *glyph, long x, long y, const unsigned char *colours)