我正在使用此处找到的示例：http ://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_01
问题是，当我指定版本高于 3 的 OpenGL 上下文时，即：
glutInitContextVersion (3, 2);
调用 glTexImage2D 会导致 GL_INVALID_ENUM（由 GLIntercept 报告）错误，并且示例的输出为空白。据我从 OpenGL 3.3 参考资料中可以看出，只有当 type 不是有效的类型常量或 target 是无效的目标时才会发生这种情况。
这是违规行：
glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, g->bitmap.width, g->bitmap.rows, 0, GL_ALPHA, GL_UNSIGNED_BYTE, g->bitmap.buffer);
另外，我尝试修改示例以调整位图大小，使其尺寸最接近 2 的幂，如 NeHe 教程（http://nehe.gamedev.net/tutorial/freetype_fonts_in_opengl/24001/），但我仍然得到同样的错误。
我也尝试过使用 GLFW 实现示例并遇到同样的问题。
我在示例中使用了不同的着色器加载代码，但着色器编译/链接都很好，如果我没有指定现代 OpenGL 版本，该示例仍然有效。
如果它有助于我的环境是：Windows 7 64 位，Visual Studio 2010
AMD HD6950 图形和 Catalyst 12.3 驱动程序。
软件库是：
FreeGLUT 2.8.0
GLEW 1.7.0
FreeType 2.4.9
glm-0.9.3.0
作为参考，这里是 gliLog.txt - 我省略了日志末尾的大部分内容，因为它一遍又一遍地重复出现相同的错误。
GL Intercept Log. Version : 0.5 Compile Date: Dec 3 2005 Run on: Fri Jun 22 15:42:05 2012
===================================================
Diagnostic: Unknown function wglCreateContextAttribsARB being logged.
GL ERROR - Function wglGetPixelFormat(0x200110ef) generated error GL_INVALID_ENUM
GL ERROR - Function glGetString(GL_VERSION) generated error GL_INVALID_ENUM
GL ERROR - Function glGetString(GL_EXTENSIONS) generated error GL_INVALID_ENUM
...
InterceptShaderGLSL::CreateObjectPost - Unknown object type 0x8dd9
InterceptShaderGLSL::DeleteObjectPost - Unable to find shader ID 2
GL ERROR - Function glTexImage2D(GL_TEXTURE_2D,0,GL_ALPHA,27,35,0,GL_ALPHA,GL_UNSIGNED_BYTE,0x73ab670) generated error 0x0500
ImageSaveManager::Save2DImage - invalid width/height on image
InterceptImage::SaveTextureImage - Error saving image 1
GL ERROR - Function glDrawArrays(GL_TRIANGLE_STRIP,0,4) generated error 0x0502
GL ERROR - Function glTexImage2D(GL_TEXTURE_2D,0,GL_ALPHA,20,35,0,GL_ALPHA,GL_UNSIGNED_BYTE,0x73ac300) generated error 0x0500
ImageSaveManager::Save2DImage - invalid width/height on image
InterceptImage::SaveTextureImage - Error saving image 0
GL ERROR - Function glDrawArrays(GL_TRIANGLE_STRIP,0,4) generated error 0x0502
GL ERROR - Function glTexImage2D(GL_TEXTURE_2D,0,GL_ALPHA,23,28,0,GL_ALPHA,GL_UNSIGNED_BYTE,0x73ac580) generated error 0x0500
ImageSaveManager::Save2DImage - invalid width/height on image
InterceptImage::SaveTextureImage - Error saving image 0
这是示例代码
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glew.h>
#include <GL/freeglut.h>
/* Using GLM for our transformation matrix */
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
/* Using FreeType 2 for rendering fonts */
#include <ft2build.h>
#include FT_FREETYPE_H
#include "shader_utils.h"
#pragma comment(lib, "opengl32.lib")
#pragma comment(lib, "glew32.lib")
#pragma comment(lib, "freeglut.lib")
#pragma comment(lib, "freetypeD.lib")
GLuint program;
GLint attribute_coord;
GLint uniform_tex;
GLint uniform_color;
struct point {
GLfloat x;
GLfloat y;
GLfloat s;
GLfloat t;
};
GLuint vbo;
FT_Library ft;
FT_Face face;
const char *fontfilename;
int init_resources()
{
/* Initialize the FreeType2 library */
if(FT_Init_FreeType(&ft)) {
fprintf(stderr, "Could not init freetype library\n");
return 0;
}
/* Load a font */
if(FT_New_Face(ft, fontfilename, 0, &face)) {
fprintf(stderr, "Could not open font %s\n", fontfilename);
return 0;
}
/* Compile and link the shader program */
GLint link_ok = GL_FALSE;
program = text::LoadShader("text.v.glsl", NULL, "text.f.glsl");
const char* attribute_name;
attribute_name = "coord";
attribute_coord = glGetAttribLocation(program, attribute_name);
if (attribute_coord == -1) {
fprintf(stderr, "Could not bind attribute %s\n", attribute_name);
return 0;
}
const char* uniform_name;
uniform_name = "tex";
uniform_tex = glGetUniformLocation(program, uniform_name);
if (uniform_tex == -1) {
fprintf(stderr, "Could not bind uniform %s\n", uniform_name);
return 0;
}
uniform_name = "color";
uniform_color = glGetUniformLocation(program, uniform_name);
if (uniform_color == -1) {
fprintf(stderr, "Could not bind uniform %s\n", uniform_name);
return 0;
}
// Create the vertex buffer object
glGenBuffers(1, &vbo);
return 1;
}
/**
* Render text using the currently loaded font and currently set font size.
* Rendering starts at coordinates (x, y), z is always 0.
* The pixel coordinates that the FreeType2 library uses are scaled by (sx, sy).
*/
void render_text(const char *text, float x, float y, float sx, float sy) {
const char *p;
FT_GlyphSlot g = face->glyph;
/* Create a texture that will be used to hold one "glyph" */
GLuint tex;
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glUniform1i(uniform_tex, 0);
/* We require 1 byte alignment when uploading texture data */
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
/* Clamping to edges is important to prevent artifacts when scaling */
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
/* Linear filtering usually looks best for text */
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
/* Set up the VBO for our vertex data */
glEnableVertexAttribArray(attribute_coord);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(attribute_coord, 4, GL_FLOAT, GL_FALSE, 0, 0);
/* Loop through all characters */
for(p = text; *p; p++) {
/* Try to load and render the character */
if(FT_Load_Char(face, *p, FT_LOAD_RENDER))
continue;
/* Upload the "bitmap", which contains an 8-bit grayscale image, as an alpha texture */
glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, g->bitmap.width, g->bitmap.rows, 0, GL_ALPHA, GL_UNSIGNED_BYTE, g->bitmap.buffer);
/* Calculate the vertex and texture coordinates */
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;
point box[4] = {
{x2, -y2 , 0, 0},
{x2 + w, -y2 , 1, 0},
{x2, -y2 - h, 0, 1},
{x2 + w, -y2 - h, 1, 1},
};
/* Draw the character on the screen */
glBufferData(GL_ARRAY_BUFFER, sizeof box, box, GL_DYNAMIC_DRAW);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
/* Advance the cursor to the start of the next character */
x += (g->advance.x >> 6) * sx;
y += (g->advance.y >> 6) * sy;
}
glDisableVertexAttribArray(attribute_coord);
glDeleteTextures(1, &tex);
}
void display()
{
float sx = 2.0 / glutGet(GLUT_WINDOW_WIDTH);
float sy = 2.0 / glutGet(GLUT_WINDOW_HEIGHT);
glUseProgram(program);
/* White background */
glClearColor(1, 1, 1, 1);
glClear(GL_COLOR_BUFFER_BIT);
/* Enable blending, necessary for our alpha texture */
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
GLfloat black[4] = {0, 0, 0, 1};
GLfloat red[4] = {1, 0, 0, 1};
GLfloat transparent_green[4] = {0, 1, 0, 0.5};
/* Set font size to 48 pixels, color to black */
FT_Set_Pixel_Sizes(face, 0, 48);
glUniform4fv(uniform_color, 1, black);
/* Effects of alignment */
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);
/* Scaling the texture versus changing the font size */
render_text("The Small Texture Scaled Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 175 * sy, sx * 0.5, sy * 0.5);
FT_Set_Pixel_Sizes(face, 0, 24);
render_text("The Small Font Sized Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 200 * sy, sx, sy);
FT_Set_Pixel_Sizes(face, 0, 48);
render_text("The Tiny Texture Scaled Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 235 * sy, sx * 0.25, sy * 0.25);
FT_Set_Pixel_Sizes(face, 0, 12);
render_text("The Tiny Font Sized Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 250 * sy, sx, sy);
FT_Set_Pixel_Sizes(face, 0, 48);
/* Colors and transparency */
render_text("The Solid Black Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 430 * sy, sx, sy);
glUniform4fv(uniform_color, 1, red);
render_text("The Solid Red Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 330 * sy, sx, sy);
render_text("The Solid Red Fox Jumps Over The Lazy Dog", -1 + 28 * sx, 1 - 450 * sy, sx, sy);
glUniform4fv(uniform_color, 1, transparent_green);
render_text("The Transparent Green Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 380 * sy, sx, sy);
render_text("The Transparent Green Fox Jumps Over The Lazy Dog", -1 + 18 * sx, 1 - 440 * sy, sx, sy);
glutSwapBuffers();
}
void free_resources()
{
glDeleteProgram(program);
}
int main(int argc, char* argv[]) {
glutInitContextVersion (3, 2);
glutInitContextFlags (GLUT_FORWARD_COMPATIBLE | GLUT_DEBUG);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA|GLUT_ALPHA|GLUT_DOUBLE);
glutInitWindowSize(640, 480);
glutCreateWindow("Basic Text");
if(argc > 1)
fontfilename = argv[1];
else
fontfilename = "FreeSans.ttf";
GLenum glew_status = glewInit();
if (GLEW_OK != glew_status) {
fprintf(stderr, "Error: %s\n", glewGetErrorString(glew_status));
return 1;
}
if (!GLEW_VERSION_2_0) {
fprintf(stderr, "No support for OpenGL 2.0 found\n");
return 1;
}
if (init_resources()) {
glutDisplayFunc(display);
glutMainLoop();
}
free_resources();
return 0;
}