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Made the OpenGL 2.1 backend use custom shaders

Edging towards OpenGL 3.

--- a/src/Backends/Rendering/OpenGL2.cpp

+++ b/src/Backends/Rendering/OpenGL2.cpp

@@ -27,6 +27,7 @@

 static SDL_Window *window;

 static SDL_GLContext context;

+static GLuint normal_program_id;

 static GLuint colour_key_program_id;

 static GLuint framebuffer_id;

 static GLfloat vertex_buffer[4][2];

@@ -35,11 +36,30 @@

 static Backend_Surface framebuffer_surface;

-static const GLchar *fragment_shader_source = " \

+static const GLchar *vertex_shader_source = " \

 #version 120\n \

+void main() \

+{ \

+	gl_FrontColor = gl_Color; \

+	gl_TexCoord[0] = gl_MultiTexCoord0; \

+	gl_Position = gl_ModelViewMatrix * gl_Vertex; \

+} \

+";

+

+static const GLchar *fragment_shader_source_normal = " \

+#version 120\n \

 uniform sampler2D tex; \

 void main() \

 { \

+	gl_FragColor = gl_Color * texture2D(tex, gl_TexCoord[0].st); \

+} \

+";

+

+static const GLchar *fragment_shader_source_colour_key = " \

+#version 120\n \

+uniform sampler2D tex; \

+void main() \

+{ \

 	vec4 colour = gl_Color * texture2D(tex, gl_TexCoord[0].st); \

 \

 	if (colour.xyz == vec3(0.0f, 0.0f, 0.0f)) \

@@ -49,12 +69,22 @@

 } \

 ";

-static GLuint CompileShader(const char *fragment_shader_source)

+static GLuint CompileShader(const char *vertex_shader_source, const char *fragment_shader_source)

 {

 	GLint shader_status;

 	GLuint program_id = glCreateProgram();

+	GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);

+	glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);

+	glCompileShader(vertex_shader);

+

+	glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &shader_status);

+	if (shader_status != GL_TRUE)

+		return 0;

+

+	glAttachShader(program_id, vertex_shader);

+

 	GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);

 	glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);

 	glCompileShader(fragment_shader);

@@ -134,9 +164,13 @@

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

-	// Set up our colour-key-enabled fragment shader

-	colour_key_program_id = CompileShader(fragment_shader_source);

+	// Set up our shaders

+	normal_program_id = CompileShader(vertex_shader_source, fragment_shader_source_normal);

+	colour_key_program_id = CompileShader(vertex_shader_source, fragment_shader_source_colour_key);

+	if (normal_program_id == 0 || colour_key_program_id == 0)

+		printf("Failed to compile shaders\n");

+

 	// Set up framebuffer (used for surface-to-surface blitting)

 	glGenFramebuffersEXT(1, &framebuffer_id);

 	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer_id);

@@ -165,7 +199,7 @@

 void Backend_DrawScreen(void)

 {

 	// Disable colour-keying

-	glUseProgram(0);

+	glUseProgram(normal_program_id);

 	// Target actual screen, and not our framebuffer

 	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

@@ -271,7 +305,7 @@

 		return;

 	// Switch to colour-key shader if we have to

-	glUseProgram(colour_key ? colour_key_program_id : 0);

+	glUseProgram(colour_key ? colour_key_program_id : normal_program_id);

 	glBindTexture(GL_TEXTURE_2D, source_surface->texture_id);

@@ -338,7 +372,7 @@

 		return;

 	// Disable colour-keying

-	glUseProgram(0);

+	glUseProgram(normal_program_id);

 	// Use blank default texture, for a solid colour-fill

 	glBindTexture(GL_TEXTURE_2D, 0);

@@ -472,7 +506,7 @@

 static void DrawGlyphCommon(Backend_Glyph *glyph, long x, long y, const unsigned char *colours)

 {

 	// Disable colour-keying

-	glUseProgram(0);

+	glUseProgram(normal_program_id);

 	glBindTexture(GL_TEXTURE_2D, glyph->texture_id);