使用 SDL2、openGL ES 2.0 (GLSL 1.0) 和 Freetype 渲染字体
Render fonts with SDL2, openGL ES 2.0 (GLSL 1.0) & Freetype
这是我第一次 post 来这里。我正在开发一个旨在在 raspberry pi 3 板上使用的应用程序。我的目标是使用 gpu 而不是 cpu 成功绘制图形，从而使后者足够可用以满足 cpu 应用程序其他部分所需的处理需求，例如数学计算，i/o comms, I2C comms, virtual serial port comms etc.
到目前为止，我已经能够使用 SDL2 和 opengles 2.0 通过 glDrawArrays() 绘制线条，除其他外，遵循来自 https://keasigmadelta.com/store/gles3sdl2-tutorial/ 的一篇论文的教程。我在启用了 GL 驱动程序的 raspberry pi 3 中成功尝试支持 openGL ES 2.0 和 GLSL 1.0。
我正在尝试使用 SDL2 渲染字体，它提供了非常好的功能，可以让您定义颜色和大小以及结果渲染的其他参数。尽管使用 SDL2 函数渲染字体 TTF_RenderText_Blended(...) 给了我完美的结果，合理的时间和 cpu 在我的英特尔核心 2 四核 9550 2.8GHz 上的开销，我不能说同样的raspberry pi 3. 尝试在我的 raspi3 上使用带有 glDrawArrays() 的 gpu 给了我令人印象深刻的结果，几乎 5-10% cpu 负载，随机选择的顶点之间有 1000 条线被绘制 > 50 次第二。但是我需要使用 gpu 而不是 cpu 来渲染字体，因为我的 raspi3 上的普通 SDL2 字体渲染导致 50-60% cpu 负载，这让我没有 space 其他数学计算等。
在互联网上搜索了 2-3 天后，我决定按照来自 https://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_01 的教程进行操作，但是其中不包括 SDL2。尽管我能够编译代码，但我在下面给出了没有错误的信息： g++ -Wall main.cpp -I/usr/include/freetype2 -lSDL2 -lSDL2_ttf -lGL -lGLEW -lfreetype -o main 。您可以排除一些选项，因为它们指的是正在使用的其他库，例如 ttf.
请记住，该代码已经可以与 glDrawArrays() 一起正常工作，尽管没有提及它。
有些人会觉得我的一些评论很荒谬，我知道。
我从以下代码中得到的是一个颜色由 glClearColor(0.5, 0.5, 0.5, 1); 设置的屏幕；这是灰色的，这正是我得到的。
没有其他事情发生。在调试方面，我在函数 renderText() 中放置了一个 SDL_Log() 。如果您注意到，display() 函数包含 2 次对 renderText() 的调用。 2 SDL_Log() 函数在应用 window:
中为我提供了以下内容
INFO: Debug info: glyph w: 0, glyph rows: 0
INFO: Debug info: glyph w: 25, glyph rows: 36
我没有更多的信息可以给你了。你能帮我完成字体渲染吗？
有一件事是肯定的。我必须坐下来学习一些 opengles 和 GLSL。
顶点着色器内容
#version 100
attribute vec4 coord;
varying vec2 texcoord;
void main(void) {
gl_Position = vec4(coord.xy, 0, 1);
texcoord = coord.zw;
}
片段着色器内容
#version 100
#ifdef GL_ES
precision highp float;
#endif
varying vec2 texcoord;
uniform sampler2D tex;
uniform vec4 color;
void main(void) {
gl_FragColor = vec4(1, 1, 1, texture2D(tex, texcoord).r) * color;
}
编译为：
g++ -Wall main.cpp -I/usr/include/freetype2 -lSDL2 -lGL -lGLEW -lfreetype -o main
源码在LinuxMint 18.3（ubuntu16.04）中测试，如下：
// Standard libs
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
// Add -lSDL2
// Found at /usr/local/include/SDL2
#include <SDL2/SDL.h>
// Add -lGL and -lGLEW to compiler
// Found at /usr/include/GL
#include <GL/glew.h>
#include <GL/glu.h>
// Add -lfreetype and -I/usr/include/freetype2 to compiler
// Found at /usr/include/freetype2/freetype/config/
#include <ft2build.h>
#include FT_FREETYPE_H
SDL_Window *window=NULL;
SDL_GLContext openGLContext;
FT_Library ft=NULL;
FT_Face face;
GLuint shaderProg;
typedef struct {
float position[2];
} Vertex;
// The function render_text() takes 5 arguments: the string to render, the x and y start coordinates,
// and the x and y scale parameters. The last two should be chosen such that one glyph pixel corresponds
// to one screen pixel. Let's look at the display() function which draws the whole screen:
void render_text(const char *text, float x, float y, float sx, float sy) {
const char *p;
FT_GlyphSlot g = face->glyph;
SDL_Log("Debug info: glyph w: %d, glyph rows: %d", g->bitmap.width, g->bitmap.rows);
for(p = text; *p; p++) {
// If FT_Load_Char() returns a non-zero value then the glyph in *p could not be loaded
if(FT_Load_Char(face, *p, FT_LOAD_RENDER))
continue;
glTexImage2D(
GL_TEXTURE_2D,
0,
GL_RED,
g->bitmap.width,
g->bitmap.rows,
0,
GL_RED,
GL_UNSIGNED_BYTE,
g->bitmap.buffer
);
float x2 = x + g->bitmap_left * sx;
float y2 = -y - g->bitmap_top * sy;
float w = g->bitmap.width * sx;
float h = g->bitmap.rows * sy;
GLfloat box[4][4] = {
{x2, -y2 , 0, 0},
{x2 + w, -y2 , 1, 0},
{x2, -y2 - h, 0, 1},
{x2 + w, -y2 - h, 1, 1},
};
glBufferData(GL_ARRAY_BUFFER, sizeof box, box, GL_DYNAMIC_DRAW);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
x += (g->advance.x/64) * sx;
y += (g->advance.y/64) * sy;
}
}
void display(void) {
// I had to add the three next lines of code because the 1st param to glUniform4fv() was unreferenced in the Wiki tutorial.
// After looking at: https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetUniformLocation.xhtml
// I concluded that i had to use glGetUniformLocation() to get the uLocation but i had no idea what to pass as 2nd param to glGetUniformLocation()
// Docs say regarding the 2nd param: Points to a null terminated string containing the name of the uniform variable whose location is to be queried.
// There is a var called uniform_location in the fragment shader so i had i pick one from there. I know i sound ridiculus...
int w=0, h=0;
SDL_GetWindowSize(window, &w, &h);
GLint uLocation = glGetUniformLocation(shaderProg, "sample2D");
// Clear the invisible buffer with the color specified
glClearColor(0.5, 0.5, 0.5, 1);
glClear(GL_COLOR_BUFFER_BIT);
GLfloat black[4] = {0, 0, 0, 1};
glUniform4fv(uLocation, 1, black);
float sx = 2.0 / (float)w;
float sy = 2.0 / (float)h;
render_text("The Quick Brown Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 50 * sy, sx, sy);
render_text("The Misaligned Fox Jumps Over The Lazy Dog", -1 + 8.5 * sx, 1 - 100.5 * sy, sx, sy);
// I replaced glutSwapBuffers(); with the following
SDL_GL_SwapWindow(window);
}
void shaderProgDestroy(GLuint shaderProg) {
glDeleteProgram(shaderProg);
}
/** Destroys a shader.
*/
static void shaderDestroy(GLuint shaderID) {
glDeleteShader(shaderID);
}
/** Gets the file's length.
*
* @param file the file
*
* @return size_t the file's length in bytes
*/
static size_t fileGetLength(FILE *file) {
size_t length;
size_t currPos = ftell(file);
fseek(file, 0, SEEK_END);
length = ftell(file);
// Return the file to its previous position
fseek(file, currPos, SEEK_SET);
return length;
}
/** Loads and compiles a shader from a file.
*
* This will print any errors to the console.
*
* @param filename the shader's filename
* @param shaderType the shader type (e.g., GL_VERTEX_SHADER)
*
* @return GLuint the shader's ID, or 0 if failed
*/
static GLuint shaderLoad(const char *filename, GLenum shaderType) {
FILE *file = fopen(filename, "r");
if (!file) {
SDL_Log("Can't open file: %s\n", filename);
return 0;
}
size_t length = fileGetLength(file);
// Alloc space for the file (plus '[=14=]' termination)
GLchar *shaderSrc = (GLchar*)calloc(length + 1, 1);
if (!shaderSrc) {
SDL_Log("Out of memory when reading file: %s\n", filename);
fclose(file);
file = NULL;
return 0;
}
fread(shaderSrc, 1, length, file);
// Done with the file
fclose(file);
file = NULL;
// Create the shader
GLuint shader = glCreateShader(shaderType);
glShaderSource(shader, 1, (const GLchar**)&shaderSrc, NULL);
free(shaderSrc);
shaderSrc = NULL;
// Compile it
glCompileShader(shader);
GLint compileSucceeded = GL_FALSE;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compileSucceeded);
if (!compileSucceeded) {
// Compilation failed. Print error info
SDL_Log("Compilation of shader %s failed:\n", filename);
GLint logLength = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
GLchar *errLog = (GLchar*)malloc(logLength);
if (errLog) {
glGetShaderInfoLog(shader, logLength, &logLength, errLog);
SDL_Log("%s\n", errLog);
free(errLog);
}
else {
SDL_Log("Couldn't get shader log; out of memory\n");
}
glDeleteShader(shader);
shader = 0;
}
return shader;
}
GLuint shaderProgLoad(const char *vertFilename, const char *fragFilename) {
// Load vertex shader file from disk
GLuint vertShader = shaderLoad(vertFilename, GL_VERTEX_SHADER);
if (!vertShader) {
SDL_Log("Couldn't load vertex shader: %s\n", vertFilename);
return 0;
}
// Load fragment shader file from disk
GLuint fragShader = shaderLoad(fragFilename, GL_FRAGMENT_SHADER);
if (!fragShader) {
SDL_Log("Couldn't load fragment shader: %s\n", fragFilename);
shaderDestroy(vertShader);
vertShader = 0;
return 0;
}
// Create a shader program out of the two (or more) shaders loaded
GLuint shaderProg = glCreateProgram();
if (shaderProg) {
// Attach the the two shaders to the program
glAttachShader(shaderProg, vertShader);
glAttachShader(shaderProg, fragShader);
// Link the two shaders together
glLinkProgram(shaderProg);
GLint linkingSucceeded = GL_FALSE;
// Get a status (true or false) of the linking process
glGetProgramiv(shaderProg, GL_LINK_STATUS, &linkingSucceeded);
// Handle the error if linking the two shaders went wrong
if (!linkingSucceeded) {
SDL_Log("Linking shader failed (vert. shader: %s, frag. shader: %s\n", vertFilename, fragFilename);
GLint logLength = 0;
glGetProgramiv(shaderProg, GL_INFO_LOG_LENGTH, &logLength);
GLchar *errLog = (GLchar*)malloc(logLength);
if (errLog) {
glGetProgramInfoLog(shaderProg, logLength, &logLength, errLog);
SDL_Log("%s\n", errLog);
free(errLog);
}
else {
SDL_Log("Couldn't get shader link log; out of memory\n");
}
glDeleteProgram(shaderProg);
shaderProg = 0;
}
}
else {
SDL_Log("Couldn't create shader program\n");
}
// Free resources
shaderDestroy(vertShader);
shaderDestroy(fragShader);
// Return the resulting shader program
return shaderProg;
}
/** Creates the Vertex Buffer Object (VBO) containing
* the given vertices.
*
* @param vertices pointer to the array of vertices
* @param numVertices the number of vertices in the array
*/
GLuint vboCreate(Vertex *vertices, GLuint numVertices) {
// Create the Vertex Buffer Object
GLuint vbo;
int nBuffers = 1;
// Create a buffer
glGenBuffers(nBuffers, &vbo);
// Make the buffer a VBO buffer
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// Copy the vertices data in the buffer, and deactivate with glBindBuffer(GL_ARRAY_BUFFER, 0);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * numVertices, vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// Check for problems
GLenum err = glGetError();
if (err != GL_NO_ERROR) {
// Failed
glDeleteBuffers(nBuffers, &vbo);
SDL_Log("Creating VBO failed, code %u\n", err);
vbo = 0;
}
return vbo;
}
/** Frees the VBO.
*
* @param vbo the VBO's name.
*/
void vboFree(GLuint vbo) {
glDeleteBuffers(1, &vbo);
}
void freeResources(void){
SDL_GL_DeleteContext(openGLContext);
shaderProgDestroy(shaderProg);
SDL_Quit();
SDL_DestroyWindow(window);
}
int main(int argc, char* args[]){
// SDL2 video init
SDL_Init( SDL_INIT_VIDEO | SDL_INIT_TIMER );
// Setting openGL attributes
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
// Enable double buffering
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
// Enable hardware accelaration if available
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
glewExperimental = GL_TRUE;
// Get window
window = SDL_CreateWindow( "Test", SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED, 800, 600, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL);
// Get openGL context
openGLContext = SDL_GL_CreateContext(window);
// Init glew
glewInit();
// ft globally defined with FT_Library ft
FT_Init_FreeType(&ft);
// face globally defined with FT_Face face;
FT_New_Face(ft, "LiberationMono-Bold.ttf", 0, &face);
// All return values of the init functions above since the point where main starts are normal. No errors are returned.
// I have skipped the if conditions for the shake of simplicity
// Load vertex & fragment shaders, compile them, link them together, make a program and return it
shaderProg = shaderProgLoad("shaderV1.vert", "shaderV1.frag");
// Activate the program
glUseProgram(shaderProg);
// The code up to this point works fine
// This is where the code from wikipedia starts
FT_Set_Pixel_Sizes(face, 0, 48);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
GLuint vbo;
// I set the var attribute_coord. Is this right? The code from Wiki did not have any initializations for this variable.
GLuint attribute_coord=0;
glGenBuffers(1, &vbo);
glEnableVertexAttribArray(attribute_coord);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(attribute_coord, 4, GL_FLOAT, GL_FALSE, 0, 0);
display();
// This is where the code from wikipedia ends
while (1){
// Wait
SDL_Delay(10);
}
// A function that free resources
freeResources();
return 0;
}
问题很简单，你忘了设置uniform变量tex和color（tex在你的情况下不是必需的，因为它默认设置为0 ).
在程序链接(glLinkProgram)后，通过glGetUniformLocation确定活动程序资源tex和color的统一位置。
通过glUniform1i分别设置uniformsglUniform4fv，shader程序变成当前程序后(gUseProgram)：
shaderProg = shaderProgLoad("shaderV1.vert", "shaderV1.frag");
GLuint tex_loc = glGetUniformLocation( shaderProg, "tex" );
GLuint color_loc = glGetUniformLocation( shaderProg, "color" );
// Activate the program
glUseProgram(shaderProg);
glUniform1i( tex_loc, 0 ); // 0, because the texture is bound to of texture unit 0
float col[4] = { 1.0f, 0.0f, 0.0, 1.0f }; // red and opaque
glUniform4fv( color_loc, 1, col);
这是我第一次 post 来这里。我正在开发一个旨在在 raspberry pi 3 板上使用的应用程序。我的目标是使用 gpu 而不是 cpu 成功绘制图形，从而使后者足够可用以满足 cpu 应用程序其他部分所需的处理需求，例如数学计算，i/o comms, I2C comms, virtual serial port comms etc.
到目前为止，我已经能够使用 SDL2 和 opengles 2.0 通过 glDrawArrays() 绘制线条，除其他外，遵循来自 https://keasigmadelta.com/store/gles3sdl2-tutorial/ 的一篇论文的教程。我在启用了 GL 驱动程序的 raspberry pi 3 中成功尝试支持 openGL ES 2.0 和 GLSL 1.0。
我正在尝试使用 SDL2 渲染字体，它提供了非常好的功能，可以让您定义颜色和大小以及结果渲染的其他参数。尽管使用 SDL2 函数渲染字体 TTF_RenderText_Blended(...) 给了我完美的结果，合理的时间和 cpu 在我的英特尔核心 2 四核 9550 2.8GHz 上的开销，我不能说同样的raspberry pi 3. 尝试在我的 raspi3 上使用带有 glDrawArrays() 的 gpu 给了我令人印象深刻的结果，几乎 5-10% cpu 负载，随机选择的顶点之间有 1000 条线被绘制 > 50 次第二。但是我需要使用 gpu 而不是 cpu 来渲染字体，因为我的 raspi3 上的普通 SDL2 字体渲染导致 50-60% cpu 负载，这让我没有 space 其他数学计算等。
在互联网上搜索了 2-3 天后，我决定按照来自 https://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_01 的教程进行操作，但是其中不包括 SDL2。尽管我能够编译代码，但我在下面给出了没有错误的信息： g++ -Wall main.cpp -I/usr/include/freetype2 -lSDL2 -lSDL2_ttf -lGL -lGLEW -lfreetype -o main 。您可以排除一些选项，因为它们指的是正在使用的其他库，例如 ttf.
请记住，该代码已经可以与 glDrawArrays() 一起正常工作，尽管没有提及它。
有些人会觉得我的一些评论很荒谬，我知道。
我从以下代码中得到的是一个颜色由 glClearColor(0.5, 0.5, 0.5, 1); 设置的屏幕；这是灰色的，这正是我得到的。 没有其他事情发生。在调试方面，我在函数 renderText() 中放置了一个 SDL_Log() 。如果您注意到，display() 函数包含 2 次对 renderText() 的调用。 2 SDL_Log() 函数在应用 window:
中为我提供了以下内容INFO: Debug info: glyph w: 0, glyph rows: 0
INFO: Debug info: glyph w: 25, glyph rows: 36
我没有更多的信息可以给你了。你能帮我完成字体渲染吗？
有一件事是肯定的。我必须坐下来学习一些 opengles 和 GLSL。
顶点着色器内容
#version 100
attribute vec4 coord;
varying vec2 texcoord;
void main(void) {
gl_Position = vec4(coord.xy, 0, 1);
texcoord = coord.zw;
}
片段着色器内容
#version 100
#ifdef GL_ES
precision highp float;
#endif
varying vec2 texcoord;
uniform sampler2D tex;
uniform vec4 color;
void main(void) {
gl_FragColor = vec4(1, 1, 1, texture2D(tex, texcoord).r) * color;
}
编译为：
g++ -Wall main.cpp -I/usr/include/freetype2 -lSDL2 -lGL -lGLEW -lfreetype -o main
源码在LinuxMint 18.3（ubuntu16.04）中测试，如下：
// Standard libs
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
// Add -lSDL2
// Found at /usr/local/include/SDL2
#include <SDL2/SDL.h>
// Add -lGL and -lGLEW to compiler
// Found at /usr/include/GL
#include <GL/glew.h>
#include <GL/glu.h>
// Add -lfreetype and -I/usr/include/freetype2 to compiler
// Found at /usr/include/freetype2/freetype/config/
#include <ft2build.h>
#include FT_FREETYPE_H
SDL_Window *window=NULL;
SDL_GLContext openGLContext;
FT_Library ft=NULL;
FT_Face face;
GLuint shaderProg;
typedef struct {
float position[2];
} Vertex;
// The function render_text() takes 5 arguments: the string to render, the x and y start coordinates,
// and the x and y scale parameters. The last two should be chosen such that one glyph pixel corresponds
// to one screen pixel. Let's look at the display() function which draws the whole screen:
void render_text(const char *text, float x, float y, float sx, float sy) {
const char *p;
FT_GlyphSlot g = face->glyph;
SDL_Log("Debug info: glyph w: %d, glyph rows: %d", g->bitmap.width, g->bitmap.rows);
for(p = text; *p; p++) {
// If FT_Load_Char() returns a non-zero value then the glyph in *p could not be loaded
if(FT_Load_Char(face, *p, FT_LOAD_RENDER))
continue;
glTexImage2D(
GL_TEXTURE_2D,
0,
GL_RED,
g->bitmap.width,
g->bitmap.rows,
0,
GL_RED,
GL_UNSIGNED_BYTE,
g->bitmap.buffer
);
float x2 = x + g->bitmap_left * sx;
float y2 = -y - g->bitmap_top * sy;
float w = g->bitmap.width * sx;
float h = g->bitmap.rows * sy;
GLfloat box[4][4] = {
{x2, -y2 , 0, 0},
{x2 + w, -y2 , 1, 0},
{x2, -y2 - h, 0, 1},
{x2 + w, -y2 - h, 1, 1},
};
glBufferData(GL_ARRAY_BUFFER, sizeof box, box, GL_DYNAMIC_DRAW);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
x += (g->advance.x/64) * sx;
y += (g->advance.y/64) * sy;
}
}
void display(void) {
// I had to add the three next lines of code because the 1st param to glUniform4fv() was unreferenced in the Wiki tutorial.
// After looking at: https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetUniformLocation.xhtml
// I concluded that i had to use glGetUniformLocation() to get the uLocation but i had no idea what to pass as 2nd param to glGetUniformLocation()
// Docs say regarding the 2nd param: Points to a null terminated string containing the name of the uniform variable whose location is to be queried.
// There is a var called uniform_location in the fragment shader so i had i pick one from there. I know i sound ridiculus...
int w=0, h=0;
SDL_GetWindowSize(window, &w, &h);
GLint uLocation = glGetUniformLocation(shaderProg, "sample2D");
// Clear the invisible buffer with the color specified
glClearColor(0.5, 0.5, 0.5, 1);
glClear(GL_COLOR_BUFFER_BIT);
GLfloat black[4] = {0, 0, 0, 1};
glUniform4fv(uLocation, 1, black);
float sx = 2.0 / (float)w;
float sy = 2.0 / (float)h;
render_text("The Quick Brown Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 50 * sy, sx, sy);
render_text("The Misaligned Fox Jumps Over The Lazy Dog", -1 + 8.5 * sx, 1 - 100.5 * sy, sx, sy);
// I replaced glutSwapBuffers(); with the following
SDL_GL_SwapWindow(window);
}
void shaderProgDestroy(GLuint shaderProg) {
glDeleteProgram(shaderProg);
}
/** Destroys a shader.
*/
static void shaderDestroy(GLuint shaderID) {
glDeleteShader(shaderID);
}
/** Gets the file's length.
*
* @param file the file
*
* @return size_t the file's length in bytes
*/
static size_t fileGetLength(FILE *file) {
size_t length;
size_t currPos = ftell(file);
fseek(file, 0, SEEK_END);
length = ftell(file);
// Return the file to its previous position
fseek(file, currPos, SEEK_SET);
return length;
}
/** Loads and compiles a shader from a file.
*
* This will print any errors to the console.
*
* @param filename the shader's filename
* @param shaderType the shader type (e.g., GL_VERTEX_SHADER)
*
* @return GLuint the shader's ID, or 0 if failed
*/
static GLuint shaderLoad(const char *filename, GLenum shaderType) {
FILE *file = fopen(filename, "r");
if (!file) {
SDL_Log("Can't open file: %s\n", filename);
return 0;
}
size_t length = fileGetLength(file);
// Alloc space for the file (plus '[=14=]' termination)
GLchar *shaderSrc = (GLchar*)calloc(length + 1, 1);
if (!shaderSrc) {
SDL_Log("Out of memory when reading file: %s\n", filename);
fclose(file);
file = NULL;
return 0;
}
fread(shaderSrc, 1, length, file);
// Done with the file
fclose(file);
file = NULL;
// Create the shader
GLuint shader = glCreateShader(shaderType);
glShaderSource(shader, 1, (const GLchar**)&shaderSrc, NULL);
free(shaderSrc);
shaderSrc = NULL;
// Compile it
glCompileShader(shader);
GLint compileSucceeded = GL_FALSE;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compileSucceeded);
if (!compileSucceeded) {
// Compilation failed. Print error info
SDL_Log("Compilation of shader %s failed:\n", filename);
GLint logLength = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
GLchar *errLog = (GLchar*)malloc(logLength);
if (errLog) {
glGetShaderInfoLog(shader, logLength, &logLength, errLog);
SDL_Log("%s\n", errLog);
free(errLog);
}
else {
SDL_Log("Couldn't get shader log; out of memory\n");
}
glDeleteShader(shader);
shader = 0;
}
return shader;
}
GLuint shaderProgLoad(const char *vertFilename, const char *fragFilename) {
// Load vertex shader file from disk
GLuint vertShader = shaderLoad(vertFilename, GL_VERTEX_SHADER);
if (!vertShader) {
SDL_Log("Couldn't load vertex shader: %s\n", vertFilename);
return 0;
}
// Load fragment shader file from disk
GLuint fragShader = shaderLoad(fragFilename, GL_FRAGMENT_SHADER);
if (!fragShader) {
SDL_Log("Couldn't load fragment shader: %s\n", fragFilename);
shaderDestroy(vertShader);
vertShader = 0;
return 0;
}
// Create a shader program out of the two (or more) shaders loaded
GLuint shaderProg = glCreateProgram();
if (shaderProg) {
// Attach the the two shaders to the program
glAttachShader(shaderProg, vertShader);
glAttachShader(shaderProg, fragShader);
// Link the two shaders together
glLinkProgram(shaderProg);
GLint linkingSucceeded = GL_FALSE;
// Get a status (true or false) of the linking process
glGetProgramiv(shaderProg, GL_LINK_STATUS, &linkingSucceeded);
// Handle the error if linking the two shaders went wrong
if (!linkingSucceeded) {
SDL_Log("Linking shader failed (vert. shader: %s, frag. shader: %s\n", vertFilename, fragFilename);
GLint logLength = 0;
glGetProgramiv(shaderProg, GL_INFO_LOG_LENGTH, &logLength);
GLchar *errLog = (GLchar*)malloc(logLength);
if (errLog) {
glGetProgramInfoLog(shaderProg, logLength, &logLength, errLog);
SDL_Log("%s\n", errLog);
free(errLog);
}
else {
SDL_Log("Couldn't get shader link log; out of memory\n");
}
glDeleteProgram(shaderProg);
shaderProg = 0;
}
}
else {
SDL_Log("Couldn't create shader program\n");
}
// Free resources
shaderDestroy(vertShader);
shaderDestroy(fragShader);
// Return the resulting shader program
return shaderProg;
}
/** Creates the Vertex Buffer Object (VBO) containing
* the given vertices.
*
* @param vertices pointer to the array of vertices
* @param numVertices the number of vertices in the array
*/
GLuint vboCreate(Vertex *vertices, GLuint numVertices) {
// Create the Vertex Buffer Object
GLuint vbo;
int nBuffers = 1;
// Create a buffer
glGenBuffers(nBuffers, &vbo);
// Make the buffer a VBO buffer
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// Copy the vertices data in the buffer, and deactivate with glBindBuffer(GL_ARRAY_BUFFER, 0);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * numVertices, vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// Check for problems
GLenum err = glGetError();
if (err != GL_NO_ERROR) {
// Failed
glDeleteBuffers(nBuffers, &vbo);
SDL_Log("Creating VBO failed, code %u\n", err);
vbo = 0;
}
return vbo;
}
/** Frees the VBO.
*
* @param vbo the VBO's name.
*/
void vboFree(GLuint vbo) {
glDeleteBuffers(1, &vbo);
}
void freeResources(void){
SDL_GL_DeleteContext(openGLContext);
shaderProgDestroy(shaderProg);
SDL_Quit();
SDL_DestroyWindow(window);
}
int main(int argc, char* args[]){
// SDL2 video init
SDL_Init( SDL_INIT_VIDEO | SDL_INIT_TIMER );
// Setting openGL attributes
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
// Enable double buffering
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
// Enable hardware accelaration if available
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
glewExperimental = GL_TRUE;
// Get window
window = SDL_CreateWindow( "Test", SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED, 800, 600, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL);
// Get openGL context
openGLContext = SDL_GL_CreateContext(window);
// Init glew
glewInit();
// ft globally defined with FT_Library ft
FT_Init_FreeType(&ft);
// face globally defined with FT_Face face;
FT_New_Face(ft, "LiberationMono-Bold.ttf", 0, &face);
// All return values of the init functions above since the point where main starts are normal. No errors are returned.
// I have skipped the if conditions for the shake of simplicity
// Load vertex & fragment shaders, compile them, link them together, make a program and return it
shaderProg = shaderProgLoad("shaderV1.vert", "shaderV1.frag");
// Activate the program
glUseProgram(shaderProg);
// The code up to this point works fine
// This is where the code from wikipedia starts
FT_Set_Pixel_Sizes(face, 0, 48);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
GLuint vbo;
// I set the var attribute_coord. Is this right? The code from Wiki did not have any initializations for this variable.
GLuint attribute_coord=0;
glGenBuffers(1, &vbo);
glEnableVertexAttribArray(attribute_coord);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(attribute_coord, 4, GL_FLOAT, GL_FALSE, 0, 0);
display();
// This is where the code from wikipedia ends
while (1){
// Wait
SDL_Delay(10);
}
// A function that free resources
freeResources();
return 0;
}
问题很简单，你忘了设置uniform变量tex和color（tex在你的情况下不是必需的，因为它默认设置为0 ).
在程序链接(glLinkProgram)后，通过glGetUniformLocation确定活动程序资源tex和color的统一位置。
通过glUniform1i分别设置uniformsglUniform4fv，shader程序变成当前程序后(gUseProgram)：
shaderProg = shaderProgLoad("shaderV1.vert", "shaderV1.frag");
GLuint tex_loc = glGetUniformLocation( shaderProg, "tex" );
GLuint color_loc = glGetUniformLocation( shaderProg, "color" );
// Activate the program
glUseProgram(shaderProg);
glUniform1i( tex_loc, 0 ); // 0, because the texture is bound to of texture unit 0
float col[4] = { 1.0f, 0.0f, 0.0, 1.0f }; // red and opaque
glUniform4fv( color_loc, 1, col);