OpenGL ES glFragColor依赖于iOS中片段着色器上的if条件
OpenGL ES glFragColor依赖于iOS中片段着色器上的if条件
提问于 2014-12-16 09:32:04
我正在写一个应用程序在iOS上允许绘制自由风格(使用手指)和在屏幕上绘制图像。我使用OpenGL ES来实现。我有两个功能，一个是绘制自由样式，一个是绘制纹理
-代码绘制自由样式
- (void)drawFreeStyle:(NSMutableArray *)pointArray {
//Prepare vertex data
.....
// Load data to the Vertex Buffer Object
glBindBuffer(GL_ARRAY_BUFFER, vboId);
glBufferData(GL_ARRAY_BUFFER, vertexCount*2*sizeof(GLfloat), vertexBuffer, GL_DYNAMIC_DRAW);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, GL_FALSE, 0, 0);
**GLuint a_ver_flag_drawing_type = glGetAttribLocation(program[PROGRAM_POINT].id, "a_drawingType");
glVertexAttrib1f(a_ver_flag_drawing_type, 0.0f);
GLuint u_fra_flag_drawing_type = glGetUniformLocation(program[PROGRAM_POINT].id, "v_drawing_type");
glUniform1f(u_fra_flag_drawing_type, 0.0);**
glUseProgram(program[PROGRAM_POINT].id);
glDrawArrays(GL_POINTS, 0, (int)vertexCount);
// Display the buffer
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];
}-代码绘制纹理
- (void)drawTexture:(UIImage *)image atRect:(CGRect)rect {
GLuint a_ver_flag_drawing_type = glGetAttribLocation(program[PROGRAM_POINT].id, "a_drawingType");
GLuint u_fra_flag_drawing_type = glGetUniformLocation(program[PROGRAM_POINT].id, "v_drawing_type");
GLuint a_position_location = glGetAttribLocation(program[PROGRAM_POINT].id, "a_Position");
GLuint a_texture_coordinates_location = glGetAttribLocation(program[PROGRAM_POINT].id, "a_TextureCoordinates");
GLuint u_texture_unit_location = glGetUniformLocation(program[PROGRAM_POINT].id, "u_TextureUnit");
glUseProgram(PROGRAM_POINT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texName);
glUniform1i(u_texture_unit_location, 0);
glUniform1f(u_fra_flag_drawing_type, 1.0);
const float textrect[] = {-1.0f, -1.0f, 0.0f, 0.0f,
-1.0f, 1.0f, 0.0f, 1.0f,
1.0f, -1.0f, 1.0f, 0.0f,
1.0f, 1.0f, 1.0f, 1.0f};
glBindBuffer(GL_ARRAY_BUFFER, vboId);
glBufferData(GL_ARRAY_BUFFER, sizeof(textrect), textrect, GL_STATIC_DRAW);
glVertexAttrib1f(a_ver_flag_drawing_type, 1.0f);
glVertexAttribPointer(a_position_location, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(0));
glVertexAttribPointer(a_texture_coordinates_location, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(2 * sizeof(float)));
glEnableVertexAttribArray(a_ver_flag_drawing_type);
glEnableVertexAttribArray(a_position_location);
glEnableVertexAttribArray(a_texture_coordinates_location);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER];
}请注意2个变量a_ver_flag_drawing_type (属性)和u_fra_flag_drawing_type (统一)。它们用于在顶点着色器和片段着色器上设置标志，以确定这两个文件上无绘制样式或纹理
-顶点着色器
//Flag
attribute lowp float a_drawingType;
//For drawing
attribute vec4 inVertex;
uniform mat4 MVP;
uniform float pointSize;
uniform lowp vec4 vertexColor;
varying lowp vec4 color;
//For texture
attribute vec4 a_Position;
attribute vec2 a_TextureCoordinates;
varying vec2 v_TextureCoordinates;
void main()
{
if (abs(a_drawingType - 1.0) < 0.0001) {
//Draw texture
v_TextureCoordinates = a_TextureCoordinates;
gl_Position = a_Position;
} else {
//Draw free style
gl_Position = MVP * inVertex;
gl_PointSize = pointSize;
color = vertexColor;
}
}-片段着色器
precision mediump float;
uniform sampler2D texture;
varying lowp vec4 color;
uniform sampler2D u_TextureUnit;
varying vec2 v_TextureCoordinates;
uniform lowp float v_drawing_type;
void main()
{
if (abs(v_drawing_type - 1.0) < 0.0001) {
//Draw texture
gl_FragColor = texture2D(u_TextureUnit, v_TextureCoordinates);
} else {
//Drawing free style
gl_FragColor = color * texture2D(texture, gl_PointCoord);
}
}我的想法是在绘制时从绘制代码中设置这些标志。属性a_drawingType用于顶点着色器，一致v_drawing_type用于片段着色器。根据这些标志来知道绘制自由样式或纹理。
但如果我独立运行，每次只有一种类型(如果运行自由绘制样式，注释代码配置顶点着色器和片段着色器文件上的绘制纹理，反之亦然)它可以像我想要的那样绘制。如果我将它们组合在一起，它不仅不能绘制，还会使应用程序崩溃，因为
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);我是OpenGL ES和GLSL语言的新手，所以我不确定我这样设置标志的想法是对还是错。有人能帮我吗？
Stack Overflow用户
发布于 2014-12-17 05:16:41
所以你为什么不在其中的一个上构建两个独立的着色器程序和useProgram()，而不是将标志值发送到GL，并在顶点中进行昂贵的条件分支，特别是片段着色器？
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/27496144
复制相关文章
相似问题
腾讯云开发者
